I wonder if it could be done where the service acts essentially as a bank but does not use fractional reserve policies. So a user A adds $100 to their account. We keep a log and add that $100 to our "real" bank account. User A then pays User B $0.01. So we keep it in our ledger that $99.99 is for User A and $0.01 is for User B. But we don't make any actual bank transactions until a withdrawal request happens. There is probably some sort of regulation around this but maybe we do it like SecondLife with Lindens and then people can cash out their Lindens later.