Action Refunds greater than 100%

With customer power greater than ever, it is now commonplace to refund amounts greater than 100% of the order value, to cover return postage costs that have already been spent out by the customer. It would be very useful to have a 'Refund additional amount' box alongside the refund shipping box to cover these extra refunds, and for StoreFeeder to then show the total value of the order as negative.