There should be a "Use all cards" button.
one button uses all your cards at once, so you don't keep on pressing "use"
This would not work as many cards (gift, abandon, blockade, spy, recon, airlift, etc) all require additional inputs while being played. Other cards like Order Delay, you want to play at the correct time. Really this only would work if you ONLY had reinforcement cards. Doesn't seem like a big time saver anyway (sounds like the game settings are screwed up if you have tons of small ones and not one big one).