I think that's certainly feasible. I know for my prototypes, anyway, two is twice as much work as one, and one is a lot of work, but then I make pretty prototypes.
I haven't re-read this thread, so I'm not sure what is written above, but I don't see any real flaws with the model where you send one prototype and the entry fee includes two postages, three if you want it back. Then at the central point two (or three) pre-paid shipping labels are generated, the first going on the outside of the box and the second (and optionally third) in envelopes inside the box. Group one finishes their assessment and grabs shipping label 2 and puts it on the outside of the box. If there's a third label, group 2 applies label 3 to the outside of the box and ships it off.
The rules could state the the prototype needs to fit into, for example, a USPS Priority Mail box and not weigh more than whatever its normal max is (which is plenty for any game, even with glass beads or such), ensuring that re-shipping will be pretty straightforward.
That was my basic thought on how to handle it, anyway.
-- Matthew
