^ (Using that same idea...) You could make him ask you for the money to buy something. Like, hold up the line because he isn't allowed to carry any money...and go find you in the store and then ask for the cash (or credit card). If you were feeling particularly fiesty, you could even go off-script and say something like..."No...you may not have the money for that. This is why you're not allowed to carry your own money. Now go and wait for me in the car." And then swat his ass.

On second thought...that might a bit much...