Something like a thermos trade would probably be the best bet. Fill the thermos with a frag, send it to whoever, then they send 1 to the next person and so on until it gets back to the original sender.
The only issue I have with something like this is the shipping cost. I can get pretty much any kind of frag I want locally and it would cost less than what the shipping for the thermos would cost. If people don't have frags available locally, the thermos thing would probably work nice.