Have you stopped caring about people's reactions and will just whip out a phone or voice recorder and sing stuff on the train or at the store or something?
there are ways of doing it quietly and professionally, and if i absolutely can't speak, i can document the idea using text alone, and indicate the notes, rhythm, and chords using an elaborate number system. it's tedious and it takes quite a moment, and autocorrect might kick my ass, but it can be done