How would I introduce this (continuing violation) doctrine to my defense?
You haven't provided enough info here to tell whether "serious and willful" would even be relative in your claim.
There is no "defense" in WC, you are either eligible for benefits based on medical determination, or not.
Has there been a CalOSHA complaint filed, can you meet ALL of conditions in the labor code?
4553.1. In order to support a holding of serious and willful
misconduct by an employer based upon violation of a safety order, the
appeals board must specifically find all of the following:
(1) The specific manner in which the order was violated.
(2) That the violation of the safety order did proximately cause
the injury or death, and the specific manner in which the violation
constituted the proximate cause.
(3) That the safety order, and the conditions making the safety
order applicable, were known to, and violated by, a particular named
person, either the employer, or a representative designated by
Section 4553, or that the condition making the safety order
applicable was obvious, created a probability of serious injury, and
that the failure of the employer, or a representative designated by
Section 4553, to correct the condition constituted a reckless
disregard for the probable consequences.

http://www.leginfo.ca.gov/cgi-bin/wa...ction=retrieve
Serious and willful is a seperate filing, and the WCAB has the final jurisdiction.

In Calif WC,"pattern and practice", or ''general business practice'' actually refers to the actions of a Claims Adm, or a TPA in providing benefits...
(l) "General business practice" means a pattern of violations of Labor Code section 5814 at a single adjusting location that can be distinguished by a reasonable person from an isolated event. The pattern of violations must occur in the handling of more than one claim. The pattern of violations may consist of one type of act or omission, or separate, discrete acts or omissions in the handling of more than one claim. However, where a claim file with a violation of Labor Code section 5814 has been adjusted at multiple adjusting locations, that claim file may be considered when determining the general business practice of any of the adjusting locations where the conduct that caused the violation occurred even if the file has been transferred to a different adjusting location.

http://www.dir.ca.gov/t8/10112_1.html
If you are claiming harassment/discrimination in employment, that is different than due to work injury. Calif provides for action under section 132(a) of the labor code, and there is a one year SOL to file the claim. WCAB has jurisdition.
The "continuing violation" doctrine overrides the statute of limitations. This is an exception to the statute of limitations which sets the maximum period which one can wait before filing a lawsuit. For example an employee who suffers from recurring acts of abusive conduct may be unable to recognize the true character and enormity of the discriminatory harassment until after it has continued for an appreciable period of time. Therefore the employee can bring action on any one of the hostile acts extending over a period of time as a new cause of action arises in each case. The continuing violations doctrine, which typically arises in the context of employment discrimination, permits employees to recover for discriminatory acts, such as harassment or promotion denials, that fall outside the limitations period, as long as part of a "continuing violation" is within the period.
132a. It is the declared policy of this state that there should not
be discrimination against workers who are injured in the course and
scope of their employment.
(1) Any employer who discharges, or threatens to discharge, or in
any manner discriminates against any employee because he or she has
filed or made known his or her intention to file a claim for
compensation with his or her employer or an application for
adjudication, or because the employee has received a rating, award,
or settlement, is guilty of a misdemeanor and the employee's
compensation shall be increased by one-half, but in no event more
than ten thousand dollars ($10,000), together with costs and expenses
not in excess of two hundred fifty dollars ($250). Any such employee
shall also be entitled to reinstatement and reimbursement for lost
wages and work benefits caused by the acts of the employer.
(2) Any insurer that advises, directs, or threatens an insured
under penalty of cancellation or a raise in premium or for any other
reason, to discharge an employee because he or she has filed or made
known his or her intention to file a claim for compensation with his
or her employer or an application for adjudication, or because the
employee has received a rating, award, or settlement, is guilty of a
misdemeanor and subject to the increased compensation and costs
provided in paragraph (1).
(3) Any employer who discharges, or threatens to discharge, or in
any manner discriminates against any employee because the employee
testified or made known his or her intentions to testify in another
employee's case before the appeals board, is guilty of a misdemeanor,
and the employee shall be entitled to reinstatement and
reimbursement for lost wages and work benefits caused by the acts of
the employer.
(4) Any insurer that advises, directs, or threatens an insured
employer under penalty of cancellation or a raise in premium or for
any other reason, to discharge or in any manner discriminate against
an employee because the employee testified or made known his or her
intention to testify in another employee's case before the appeals
board, is guilty of a misdemeanor.
Proceedings for increased compensation as provided in paragraph
(1), or for reinstatement and reimbursement for lost wages and work
benefits, are to be instituted by filing an appropriate petition with
the appeals board, but these proceedings may not be commenced more
than one year from the discriminatory act or date of termination of
the employee. The appeals board is vested with full power, authority,
and jurisdiction to try and determine finally all matters specified
in this section subject only to judicial review, except that the
appeals board shall have no jurisdiction to try and determine a
misdemeanor charge. The appeals board may refer and any worker may
complain of suspected violations of the criminal misdemeanor
provisions of this section to the Division of Labor Standards
Enforcement, or directly to the office of the public prosecutor.

http://www.leginfo.ca.gov/cgi-bin/di...file=110-139.6