I wonder if the answer is to have levels within the pledging system? If you pledge only one backer we take x% or cents. If you back 2-10, we charge this x-t% or cents. If 100, no charges at all. This will provide incentive to people to back more creators too.
The solution is Patreonpoints. Sell vouchers and let supporters allocate those vouchers, lock the exchange rate to the currency used to purchase the vouchers and build the service fee into that exchange rate.
This is a much smarter idea, because it also locks their money into Patreon once they've stocked up on points to spend. Not sure why they didn't go this route, to be honest.
The points make it easy to build in the service fee. Public transit here maintains an “account balance” in USD, you set the max and when your account dips below what is required for fare it refills to that max.
Steam does some something similar with an account balance but I don't think it refills. I believe a lot of businesses have a similar concept. I think you can maintain an account balance at Amazon (and probably other retailers) too.
