Not knowing much about how soundcards work, I imagine it would be feasible to flash some soundcards with custom firmware to use the speaker port for input without the user knowing.
Example https://m.youtube.com/watch?v=1NNP6AFkpjs
:-)
I've seen some theatrical DJs bring a cheap pair, snap them in half, and then use them like a "lollipop." Crowd eats it up. Even older school: using a telephone handset: https://imgur.com/a/1fUghXY