The only other answer is to find an used truck with the "factory" controller already there.
I am sure not going to buy a NEW truck knowing that there my be other things that "Can't be done"!
GM would make a killing of they would make a factory aftermarket controller.
They need to get smart and not roll over and play dead with "Cant be done"!
Its sad to say that all the GM engineers and technicians can not figure out how to add a factory trailer brake controller to an existing vehicle.
I have the dash switch and pigtail (wiring harness).
GM says "it can't be done"!
Bull crap! If its physically there from the factory why can't GM mirror the parts and procedure??