Try to reschedule the oral swab?
What happens to the gnome if the results of the swab come back "dry" or "inconclusive"?
Blah blah, it goes without saying, that if getting caught taking benzodiazepines would mean "career suicide", one should avoid doing so. No high is worth losing a job, nay, career
There's a chance
it won't show up on the oral swab, because oral swabs are supposed
to only pick up more recent usage of drugs
. The gnome might get lucky.
But as far as I know, there's no way to "get over" on an oral swab test, save for not letting the swab actually touch one's cheek. However, oral swabs have "tabs" on the bottom of them, so if the tester is actually paying attention to the testee, they can tell it's not in the correct position & would then likely come over & help correct it for the testee.
Sorry the news isn't better, but I hope this helps (in some small way)!