I like that idea, towing it to his address. Two problems, I don’t have his address, and since he has the keys, I can’t secure things down. But, it’s a starting point.
Assuming you have all the money (e.g. no chance the check bounces), I would give him 24 hour notification to remove or it will be towed to a recovery lot. He can pay them for storage and get it out.
Let him deal with them, not your problem anymore. I wouldn’t want the headache.