While taking a trip down memory lane, re-reading some old Thrax interviews recently, I read that Charlie has said he'd LOVE to be on the show - being the Simpson's freak he is - but you have to be asked versus doing the asking and they haven't been asked yet. Now, keep in mind this interview was OLD just like I said. I'd say anywhere between 1-2 years old so this post may be inaccurate but this is as far as I know.