Those of you who frequent Counterparty Github pages (https://github.com/CounterpartyXCP) may have noticed that there's a Bountysource link in each issue.
Issues can also be browsed here: http://bountysource.com/teams/counterparty/issues (if you click on Advanced Search you can filter projects, e.g. show only Counterwallet issues).
Anyone who'd like to buy himself a feature can open a free Github account, create enhancement request (or submit a bug, if it hasn't been submitted yet) and then sign in to Bountysource using the same Github account (or different, if you prefer) and place a bounty on the bug you just created. It's possible to pay with BTC.
I tried this by placing a small $5 bounty (in BTC) on one minor GUI improvement request (I just sent my BTC payment, now I'm waiting to see whether it'll register).
Bountysource isn't great (it has quite a few annoyances - people get paid in US$, they can't split bounties, and I think you can't recover BTC for bugs/requests that never get solved) but it's the best that's currently available and offers Github inteigration. Also, nothing prevents you from using any other bounty site and posting a link here.