In a futarchy, you accept people's tokens (ETH) and issue them pairs of tokens, one if which pays out if one thing (A) happens, and one of which pays out if the other thing (B) happens. They can then trade the two tokens independently against the underlying asset (ETH), and you can get an idea of what The Market thinks is going to happen (A or B).

Since contracts know what fork they're on, we could do this with the hard fork. Write a contract that takes ETH and spits out ETHD and ETHC. After the fork, on the DAO fork the contract will send all its collected ETH to the holders of ETHD, and on the Classic fork the contract will send all its ETH to the holders of ETHC.

Before the fork, both assets can trade against plain old ETH on the unforked, original chain, and by looking at their prices we can get The Market's opinion on how the hardfork is going to work out for each chain.

Anyone want to volunteer to code this up? I'm not exactly a Solidity expert, and we only have a couple of days.