How about buying some tire deflators
http://www.staunproducts.com/tire-deflator-features.php
Then just find the car, screw these bad boys on each tire in less than 5 minutes and walk away. When he comes out he'll have 4 flat tires. Not only won't he be going anywhere but he'll think he has 4 flats.
What would be really smooth is coming back an hour later and taking the caps back. If he hasn't noticed.
