Those double drive thrus can be a pain.... especially when people can't drive

Knee pads are a good idea. you should also try alternating ice and heat on your knee at night when you get home and have these aches.

What kind of floor do they have? if it is like most places it is probably that God awful cement flooring. Do they have those rubber standing pads for you? that can also help prevent further agitation to your already sore knee.

I don't know how you feel about pain meds... but Ibuprofen does wonders for that kind of knee pain as well.

Good luck... knee pain can be a bugger