Have you tried getting one of these to use when your in the car? Maybe hook your phone up to the stereo so it can play it louder or just directly through your phone pointed at the the drive up box?
I recommend that one because it has USB charging. You should be able to just plug it in and go without a charge.
Ill also ask my brothers GF how she handles the drive through. Ive got a paralyzed VC but the other one is still good (for now)
Someone previously posted successfully using the Arteck HB030B Portable Wireless Backlit Keyboard
ARTECK HB030B (I believe they also make a full size keyboard with a numeric keypad as well)