The guy can unlock it himself. Just tell him to go to the SCT website and download the "Liveload" program. That has an option to unlock the device so it can be used on another vehicle. Tell him to send you a "screen print-out" (Print Screen button) by email to confirm that it has been unlocked.
Once a tune is loaded into the car, that unit (be it Predator or XCal) is married (VIN locked) to the car.
Doesn't matter if it's an out of the box tune or custom tune.
Either way, the car will need to be re-flashed with the stock tune, and the unit unlocked in the PC software.
Same with Xcal...I actually tested it first hand using my SCT Flasher and an F350 Powerstroke. I of course loaded the respective tune for the correct vehicle. I dont have the sct software, just the program on the sctflash.com site..