Staying in tune with *oneself* is not a "ridiculous" idea; it a common & reasonable aspiration of individuals & choruses that sing unaccompanied. The director of my glee club in days gone by called it "intonation", and he policed it by repeating at the end of the song the piano chord he had played to start us off -- embarrassment enough. It is achievable even by those without perfect pitch.

If I may make a constructive suggestion to those who want bone conduction and do not have an internal finger like me (see my preceding post): one may always use an earplug. A few people may notice when you put it in & take it out, but it is far less conspicuous than keeping a finger there.