Lil' Rush

I went and saw Rush this weekend. My favorite part of the show? As always, Rush puts on a rockin' show with crazy cool lights and things going on to watch. Their new tour has South Park in their own band, Lil' Rush, doing their version of "Tom Sawyer". What none of us could figure out, though, is it from an actual episode? We have about two thirds of our DVR filled with South Park episodes, so we should know this. If you know, please tell me!!