This one time, at band camp, I shoved a flute...in front of my Rock Band mic and beat "Avenged" by Sevenfold on Expert. And so this spunky young lady has done just that, by playing her flute into the standard Rock Band microphone with the correct pitch and notes she was able to score a 98% on expert.
It's quite impressive...and quite lovely. I wonder if this works for Guitar Hero 5? You could get a group of four completely unique instruments together to play four vocal tracks at the same time in the game's co-op mode. My vote? Xylophone, Ukulele, Jew's Harp, and Bongos.