You can only do that if you are the owner of the vehicle with current CA registration. Which he is trying to transfer it to his name and get registered in CA.
You should probably look into getting a temporary plate from the state that you're in and be able to drive it from California to you for a few days that the temporary plate is good for.
If he got pulled over, he can show the Officer his driver's Minn. license, papers and tell him he is taking the car home. The Officer would just send him on his way.
