According to Dark Horizons.com & TheRaider.Net, Ian McDiarmid is apparently playing a role as "Professor Levi" in KOTCS - . He previously played this same character in an episode of Young Indy Chronicles: "Paris, 1916"
Holy crap ... I've been Netflixing the Young Indy series (seeing them for the first time) and I just watched that episode last week. He cameos as a friend of Dr. Jones Sr. who lives in Paris and young Indy stays with him for a couple days; from the name and accent I'd guess he's a German or Russian Jew.
Very interesting link if true. There are about 40 years between that episode and KCS, whereas McDiarmid has only aged 16 years in the real world. Then again, if he can play an 80+ year-old Emperor at 39 and that same character again as a middle-aged man twenty years later, I suppose anything is possible.