I got bored and made a video showing both the game and web cam on how to do it. You want to press back over and over as fast as you can without performing a backdash. You also want to make sure you're not tapping back with each input.... you want to hold the back button until you have to repress the back button again.
I've actually found some uses for this, you can make jump ins whiff allowing a free trip guard punish (b22). You can easily bait Black Adam's lightning cage (shuffle out of range of the cage, and b22 punish). It's pretty fun!
