I thought about a number of persuasive methods, but he was so delighted at being able to drive his car I didn't have the heart to take it off him even for a minute unless he was definitely and absolutely too-badly-off to drive.

I think that stealing the car keys off him would have been funny. He can't run, but my dicky hand won't let me grab. So it would have been a great chase scene - me trying to trip him up in all kinds of inventive ways that would cause the keys to come flying out onto the ground where I could get them.