the slap reveal was made by Stewart Judah
Well....unless he came up with that move before he was 8 years old I am pretty sure it was someone else. The move is mentioned in Erdnase: Legerdemain, Favorite Methods For Terminating Tricks, Leaving Selected Card in Hand of Spectator. Erdnase isn't great about citing his sources, not his fault really. Many moves originating before the 1930s are very hard to track down. That is the earliest mention that I know of of the revelation you describe...as for the trick building up to it I can't say?