That's the way to do it. Trade your stock parts for their aftermarket parts.
If someone needs tires on a car they are not turning in (gassers, even) a person that just put new tires on the car they are turning in could swap with them for a little cash.
I have aftermarket headlights (Bi-Zenon projectors with LEDs, similar to Golfs) that I would like to sell before the car goes back. I've also got fog lights and a skid plate. VW has no use for them, so why waste it all?
What I would probably do, if the cars are going to be checked before being turned in, is go to the dealer and let them do the 2306 recall. That will wipe the tune, and should reset the count to not show it has been tuned.
I might have to do it before they do the "fix", should I choose to go that route. I guess we will have to see if they decide to care. That recall said that if your car is modified they would charge you to set it back to stock, but if it is merely tuned they just overwrite it.