Who's going to build the mobile application that monitors the user's location (via GPS) and automatically sets the wireless NIC's MAC address to a specific value whenever the user is near one of these stores (and isn't connected to a real wireless network)?

Surely having a handful of shoppers who all have the same MAC address in one store at one time would screw up their analysis a little bit, no? It would certainly make it much more difficult to track a specific individual.