I've wondered this for a while!
Has Jimmy Cauty ever done any lyrics on KLF tracks?
He only appears as a "wah-wah" guitar in the outro of "Burn the Bastards" on "Shag Times", from the early days. And, to the best of my knowledge, he doesn't appear on anything, not even "Eternity Project One". Kingjelly's "The White Room" soundtrack bootleg features a snippet of Bill and Jimmy speaking about "The White Room" movie from "Snub TV", but I don't suppose that counts. I suppose the only other example may be the chorus of "Doctorin' the Tardis", which is certainly a male voice choir (of some description at least) that may have included Rockman. Plus, he can be seen miming the words on TOTP (which he also does to "Ancients of Mu" from "3 AM Eternal", on the same show two years later). John Not Scots, just Scott-ish
"Hey Rockman, this party's crap, do you know any others?"
(Womwaahwomwaaaahwom)
"Yeah, well let's get there before the booze runs out and the chicks have gone ..."