I think it's tricky, because it's pretty complex in the background to get it right based on type of card, transaction amounts, etc... A blanket amount might get a merchant in trouble if they're overcharging for the surcharge amount (and undercharging loses you money, of course). Not sure if all providers do it, but compliance on surcharging is worth looking into. Beyond Payments, Smartpay.... There are a few that look to facilitate a surcharge, but I don't think all care about keeping you on the right side of being legal. Tyro seem to leave that landmine up to you .
Sorry, that probably doesn't answer the doing it in Square option, but as the other answer here - seems like a waiting game.
