Unfortunately they are largely corporate, which is how they can sell items for such a cheap price. The store manager probably has zero say in nearly anything. Even if they wanted to "break the rules," I doubt they could make use of your connection as a backup, but I've also worked for smaller companies that were able to sell internet access to individual locations like Denny's and various large hotels in the US. Being able to somehow share sales would be the difficult part, since all sales are reported back to corporate.

Good luck if you make this work for you, it would be exciting to hear about if you're able to get them to work with you.