havent tested this myself lately, but this is how it used to work. get in the car, and have a friend in there for invite only. have your mate pin you against a wall so the character cant exit the vehicle. leave the game, and have your friend re-invite you as your other character, the one you want to car to go to.
once your other character has spawned, go over to the car and kill the dude inside it (should be a dupe toon of your other character) and take the car, drive it home.
this used to work because the cars are all attached the same account, so its not necessarily duping it, only you can take it. the game recognises your ownership, just so happens its your other character storing it.
feel free to try, although this may have been fixed now. definitely worked in the past.