This is governed by 6700:
You can drive it here legally but you would not be able to use it "for regular use on the highways of [California]." If you are storing it for him and only using it occasionally, that is fine. If the vehicle is your daily driver and the reason you are doing it is to avoid the high CA taxes, you are breaking the law. Can they prove that beyond reasonable doubt? Maybe. Maybe not. Would probably depend what you told the citing officer. If you are written a citation for it you have the legal right to ask that they prove it to the court. It's your choice.
If you decide there is a way for you to do this legally, make sure you put yourself as the lien holder.
