Do people with gastric-bypass surgery blow a higher breathalyzer level?

The volume of the stomach has no direct effect on breath alcohol. It could cause alcohol to enter the bloodstream a bit more rapidly, which could make the initial BAC rise more quickly. However, over a period of an hour or so, there should be no appreciable difference from anyone else, given the same intake.

That said, total body mass is a factor. An obese person might actually have a somewhat lower BAC for a given amount of alcohol, since it would be distributed throughout a larger volume of body fluids.

The big question: why would anyone whose health is already so compromised want to drink at all, unless they have issues.