If the 360/PS3 controllers didn't absolutely blow for the purpose, I'd suggest checking out Rock Band 2 Deluxe and the "pad is guitar" modifier we added, which restores GH2-style gamepad play for guitar (and for shiggles we added another that does "pad is drum", although button mappings are kinda funky).
Yea, I knew that. I was mentioning that it's possible to play RB2 in the same fashion.
"We" are a small team of people who make mods to older Harmonix games. RB2 Deluxe is a free patch for modded 360/PS3 that adds a lot of quality-of-life features to the game. https://rb2-deluxe.neocities.org/