Mabey I'm looking at this wrong but,what about offering to help him get his licence and insurance in exchange for not riding it untill he gets his licence.
A contract that if he rides it then it's sold period end of contract.
If he's not intrested then just take the wheels off and tell him he can have them back when he gets things in order,don't tell him his mom asked you to do it,tell him it's that or you will call the cops on him.So what if the little prick hates you .