You don't need to "live" with the relatives, just keep the car there. You won't want to buy the car for a relative due to a gift tax due on the value over $11,000, plus the sales tax. When "regifted" back to you you'd owe another gift tax and sales tax. Yes states can charge sales tax on cars when they are gifted to you. You need to buy and keep the car in your name, you'll only pay the original purchase sales tax. Lots of people keep cars at their vacation homes out of state so this is not an unusual thing to do. You merely need to register it with the other state and make sure it is insured properly to cover the drivers who are helping you put on the first 7,500 miles. When you bring it into California you'll need to reregister it (eventually) and pay a relatively small car import fee (if they still charge it anymore). No sales tax will be due as long as you can prove you already paid it when you first bought the car.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold