Tip, Swipe, Sign and Receipt with Pre-auth being used.

Currently, if using pre-auth, when going to the payment screen, you can only sign and select a receipt option on screen.  It would make sense to also be able to select a tip.  In our area, bars all want to pre-auth cards but it's not ideal for the bartender to have to ask a customer how much they want to tip in order to hit Submit so they can sign on screen and select a receipt option.  The flow we are trying to use is bartender hits submit on existing pre-authed tab, turns the display around and the customer tips, swipes, signs and emails/prints receipt