I had that happen at a Starbucks drive-up. The guy at the window told me I wasn't allowed to leave via the driveway, either, and I had to pick my bike up and carry it through the flowerbeds out to the parking lot.

Rode my bike to a small local drive-up coffee cart on the other side of the lot, asked if they served cyclists. "Of course!" the barrista said. I ranted about how Starbucks had just treated me, and she gave me a discount... Awww, I love local businesses!

(if drive-ups don't allow bikes they really should post that where it can be clearly seen before the rider gets into the driveway)