Then maybe try to apply more pressure.

Where I live we have a local bike club of about 150 people. One day, one of my friends that is an avid commuter tried to go through the drive in teller at the local credit union. He was told that he could not do that on a bike and they refused to serve him. Well, it just happened that this guy was also the public relations officer in the bike club. He wrote a serious, but friendly letter to the credit union expaining that he was a customer like anyone else, and that he had just as much right to 'drive' his bike through the drive thru as anyone else. He asked the credit union to clairify why they would not allow bikes and suggested that in the absense of any good reason, they make their employees aware that bikes WERE allowed.

His letter was very well written and businesslike. It made no overt threats, but certainly getting such a letter from a club representing hundreds of people can be threatening in its own way. A week later, he and the club received a polite and apologetic response from the credit union and he has not had a problem since.

You might take the same tactic with the store.

Dave