Ask whomever is going to do the job, if they'd mind returning the rotors and calipers to you AS THEY ARE REMOVED from the vehicle...
You would have to be there waiting as the parts were removed.
If someone is trying to pull the wool over your eyes, your making of a request like the above will make their hair stand out on end. If the service manager tries to give you any flak over your request, move on down the line.
This is not the same as asking that the old parts be returned as you pick up the vehicle. It is specifically a request for them to bring the parts to you as they are removed. It costs them nothing to bow to your request. Let's see what they say. Call it contriving your own B.S. Detector.