Johnny Depp apparently dabbles, Winston Churchill was a keen magic enthusiast, and anyone else I knew of has been mentioned.
FYI, Piven didn't execute those cuts and flourishes... He had a stand-in (I believe one of the Bucks stood in, though that may have been hear-say).
Anyone that saw the footage of him doing a card catch effect for the host and guests of a TV chat show in the US would attest to his lack of ability with SoH. Bloody good actor though.
CL
You are quite right--indeed the one of the Buck twins did stand in for Piven. I believe it was Dan. Unless it was Dave. I know it was one of those two...