A few guys considered something like this on the VW (or was it Audi?) board a few years ago and ran into the following issues;
Who "owns" the device?
How do you assure that the person who has it will actually send it on? How do you know they are who they say they are.
Who pays for postage? How do they pay? Remember it has to be insured so you're looking at a minimum of $20 each time.