The film was originally going to be an actual musical, with the song "I'm Going To Go Back There Someday" from The Muppet Movie making its return, this time, in reference to Gonzo's ambition to find his family. Then someone said, "Naaaaah! 70's funk!"note It is on the soundtrack album, though.
According to IMDB, the band Ween wrote an Image Song for Gonzo, entitled "Eye To The Sky" or something like that. They sent it to the people making the movie around the time the "70's funk" decision was made, and were then asked to do a cover of "Brick House", to which they declined. (The original Commodores recording plays at the beginning of the movie.)