trouble is you still have to queue to reach the bit where you either pay with cash or debit/credit card, or use your telepeage. paying by card is usually quicker and there are generally more lanes dedicated to card payment. just shove the card in and it pops straight out again having registered the card details, there's no waiting for the person in the booth to tell you how much it is, handing the cash over, waiting for change, waiting for the person to lift the barrier. they all accept british credit/debit cards now, as do the vast majority of card-only fuel lanes in french garages.
as far as i'm aware there's no other way to pay. we travel quite extensively in france.