Feature Request for Supporter 3.0 plugin

Is there a way to add the feature to allow users to "buy" credits on a site using the supporter plugin to use between the users and a percentage is charged for the service? Example, user signs up and has services/products that they want to buy or sell on the site at a discount 2 credits for $1. They load up the credits and go looking at the other user pages to buy the services they are in need of. My site charges a percentage and they all have a way to exchange services/ products at a discount.