I think you're right. Let's start (and most likely stop) there.I am assuming the BCM has to be programmed
The way things work now, it's not a case of the tech connecting a scanner and changing some options. The tech connects the car to his computer, which then uses the internet to contact the GM "mothership". The programming sent down from GM is based on the car's VIN. That in turn will program the car the way it came from the factory.
So, unless there's a factory kit for the upgrade (like there is for fog lights), there's no way to add the option to that VIN.
There's been a few people who've done add-ons, but when you quiz them on details, they go silent. I suspect what they've done is found a VIN that has the combination of options they're looking for and with a rogue GM tech, changed the VIN in all the modules of the car. (All the modules have to be changed, otherwise the car acts like it has stolen parts installed.)
So, a upgrading to a factory style system is not for the faint of heart. I don't know if there's any third party add-ons. If there are, they might be a safer bet. I've heard of ones that allow remote start on a car that's not equipped for that. It seems like it's the same problem - how to fool the car into starting without an actual key.