[I do not have experience with your CA situation]  But for IRS efile works well with 4852 as long as you have the EIN

Enter the W-2 info on the normal W-2 worksheet. About half way down the page there is an area to explain how you got the amounts and what you have done to try to get the real form, then link to the substitute 4852. 

Intuit says that they mark the W-2 as non-conforming and do not send the 4852 (4852 is available for paper copy)

Maybe your client can phone his employer/former employer for the CA EIN#  or get the # former another co-worker who has their real W-2?

Good Luck