You've over-estimated the ability of a convenience store manager to comprehend or care. It's probably beyond his control anyway. Some dude at corporate who does things differently designed the station so you'll need to get to him to make any changes (BTW, he doesn't care either). What you've described though is a situation that you don't control and how you'd fix it if you were the minimum wage employee in charge of the coffee station.

Personally I wouldn't drink coffee from 7-11, WaWa (don't have those here) or a bus terminal. Why not bypass the coffee station entirely and brew your own at home? When I was into coffee I ground my own beans and filtered the water to get rid of any chlorine taste and metals that come with tap water (I made a great cup of coffee). Then you can get one of the many stainless steel 16 oz coffee travel mugs and take it with you instead of adding to the waste by crushing yet another styrofoam cup (which adds its own chemicals to the brew). Think of the stainless mug as a piece of kit

BTW, I used honey in my coffee, mellower flavor, doesn't give the same sugar spike.