Episode #512 - Mitchell - Starring Joe Don Baker. A skinny, bearded man is onscreen for a moment. Host Joel Robinson quips, "It's Jim Henson!" The robot puppet Tom Servo responds with an impersonation of Kermit, saying "Hi ho!"
Episode #605- Codename: Diamond-Head- A failed Hawaii Five-0 esque TV pilot, the reference is very similer to the one in #512, above, when one of the Coast Guard officers, who is also a skinny man with a beard appears on-screen.
I took a screen cap of the Jim Henson looking guy for an icon that I decided not to make because the sillouttes wouldn't show up well and its been so long I can't remember where exactly it's from. I know for sure it's not "Mitchell" because that's Mike in the shot. Besides I don't remember a Jim Henson reference. I remember the shot being from "Angel's Revenge" also a season six episode.
This is driving me crazy...