Can't you tell them how much to fill it and not to top it off? Just do the math and keep it at 3/4 full.

I used to live in Oregon, but that was before I was old enough to drive.

My old 71 Dart would sweat gas down the quarter panel if overfull on hot days. Paint wasn't that great, but still annoying. Helps if you don't park the car with the gas cap facing into the sun.