Actually Susan Stroman spoke about "Break a Leg" on The Producers DVD commentary. She said that "The audience claps so loud that you have to take a deeper bow at the Curtain Call making you fall over and breaking your leg."
In the movie (and the play, of course) of The Dresser, the entire curse-removal is played out by Sir and his dresser (Tom Courtney) when Sir inadverdantly quotes from it.