There is a sales tax exemption for purchases delivered to the buyer out of state.
Pub 52 describes the process of avoiding use tax (same rate as sales tax) by demonstrating that the use of the goods purchased will be outside of the state.
The california resident can register the vehicle in California at the DMV and not pay sales or use tax with the proper documentation being submitted.
After the test period is over, the BOE will require supporting documentation for the exemption or will require the tax to be paid plus penalties.
I have an exemption letter from the BOE, but it was achieved when the test requirements were much easier.