My vision, when payment windows is opened and the credit card is selected, the credit card button applies the surcharge.  Granted, a "SIGN", indicating the surcharge and or customer notification at time of check out is needed.  Shouldn't be a problem to place the surcharge in with the credit card selection button, since it carries the balance over from the invoice to the balance due window.  I know, lots of code to implement, reports to change.  MORE COFFEE.   RAGE.......