I don't know about where you live, but in certain parts of NYC and the South messing with someones car in a parking lot can get you shot.
If economic times were better I could see shopping centers offering a roving tire inflation service to their shoppers. When someone parked they could be offered a pressure check and fill as a free service. It should probably be only to manufacturer's recommended pressures, but that would still save a lot of gas. There could even be a little computer print-out of their tire pressures before and after, and estimated fuel savings. Neat idea.