that would probably do, just lower the water level so that the mug breaks the surface. It seems to make them more secure being at the surface if they can be under something. I imagine they feel less exposed to predation. also, if you want to just leave him, he will be fine not eating until you return, especially if the swim bladder is the result of constipation (also possible). Bettas can go quite a long time without food, a week won't cause him any problem.