Thanks for posting that, Pete. I was just reading about that exact same act yesterday in a biography of Orson Welles.
In Welles' "The Mercury Wonder Show for Service Men," Rita Hayworth, who had rehearsed for 16 weeks, was the original assistant whom he sawed in half in his live show. Harry Cohn, the head of Columbia Studios, forbid her to appear in any more shows since she was under contract with him, so Marlene Dietrich filled in. That's how Dietrich ended up in the movie, "Follow the Boys."