Not only alcohol, there's more.....
"the way someone acts, a smell (and not just of alcohol, mints is a give away) "
Perhaps rather than take breath mints, to avoid a bus driver report, it would be preferable for the whole crew to turn up with "dragons breath" in the morning.
Mouth wash is out of the question as most contain alcohol and might fail a pc plod breathalyser. (With zero BAC)