It appears that the decision to itemize or take the standard deduction on your California state income tax return is independent of the decision to itemize or take the standard deduction on your federal income tax return.
The CA FTB Instructions: Form 540 https://www.ftb.ca.gov/forms/2016/16_540ins.pdf, page 11, address the procedure to be followed if itemizing on the CA return after having chosen to take the standard deduction on the federal return, but are silent as to the converse. There is no clear prohibition against itemizing on the federal, then taking the standard deduction on the CA return.
As you have already noted, the CA requirement for spouses filing separately mirrors the federal requirement: "If married/or an RDP and ling separate tax returns, you and your
spouse/RDP must either both itemize your deductions (even if the
itemized deductions of one spouse/RDP are less than the standard
deduction) or both take the standard deduction."
