This service is well known in car theft investigations except the cameras are supplemented with the ability to remotely cut the engine. Follow the car until it's safe to storm it. Boom goes the dynamite. http://en.wikipedia.org/wiki/Bait_car
I've watched a few episodes of the "Bait Car" show on cable and should have mentioned it above. The Wikipedia article suggests that my proposed scheme would not constitute entrapment. I wonder how much time would pass, on average, before a criminal would take a laptop from an unlocked vehicle in a "nice" part of town?