If Bitcoin network fees get higher than shipping costs, it would make sense to start giving participants physical goods for their signature campaign participation. I think it would be cool and probably help cut down on abuse if people had to give their mailing address to be a part of the campaign. Maybe try shipping some silver?
Why not just send them physical bitcoin wallets? Order some bitcoin cheques from a 3rd party. Load them with cash using low-fee transactions [just put the lowest fee over and over until it goes through to preload a bunch of cheques]. Make payout amounts for people to work toward and then mail them that many checks.
It's almost like cash, but not?