Credit Card Fee

Please add the ability to add a credit card fee. For example, under the payer when entering the information, have a checkbox to turn on or off and when you create an invoice it auto-calculates that fee we specify in settings (i.e. 2%). Currently, I have to go through and add an expense, and it looks strange attached to that specific shift on the invoice. I also think it is hard to remember all the time to do and is time consuming. Our other system allowed this feature, and it made it so easy.