How does he have the thermostat in the kegorator set now?? I'm using a freezer top fridge (10 cubic Whirlpool) for my kegging (hops are kept in the freezer) and it's able to get as low as I want it (easily to the low to mid 30's if I wanted). I'm aiming to keep mine in the 40F range since I like my brews at that temperature. I have sensors in the fridge, with displays outside (wireless units) to tell me what's going on inside it without needing to open the door. In fact, typically the only time I open the door is to either change a keg, or clean a line after changing a keg. I also have thermometer strips on my kegs, so I can see what the temp is inside them (or as close as I can get).
If he's adjusted the unit as low as it goes, and it's still not cooling lower, he might want to get it serviced before tossing money into controllers. If its' still under warranty (you didn't say how old it was, if he got it new or used) then it would be worth it to place a service call. I'm pretty much SOL there, since I voided the warranty when I drilled the holes for the gas bulkhead fittings.