Alice asks the widely respected Malice to create a feed that noone can fix her problem and she bets on it.
Bob bets against her and gets to work. Upon presenting his work to Malice, she resolves the bet in his favor.
(I find that 10% fee freaking ridiculous. I rather take my chances and risk the entire amount with someone who seems even remotely respectable (or more than than) than pay a 10% fee).
If you want to pay me a small(er) commission I can be your Malice
Another way could be multisig. Does it work with Counterparty main-net yet? E.g. ten respected members of the CP community could hold one key each to a bounty address. To pay out a XCP bounty three of them would have to sign.
When Alice issues a bounty on the bug she wants resolved, she transfers some XCP to the bounty address and explains the bounty here on the forum.