The Jedi Mind Trick is great but 100% timing-based, this video is one of the best breakdowns of the mechanics. Its not starting in the exact position you described bu even though Paul is creating the sweep you do exactly the same just setting the hook before they back-step.
My timing is lousy though and i always have the top leg looking for a knee torque so usually don't get my foot switched in time unless its somebody i know will definitely back-step. I've far more joy using Philippe Della Monica's main Reverse Half sweep he shows here.
The other thing i'll often do in the gi is pass the lapel through their legs to my under hook hand as soon as they enter my half guard. If they back step then i'm not too bothered as i'll immediately swap it to my other hand, turn towards them and start to try come up. You can keep their leg elevated and their hips turned away using your arm with the lapel as a frame as you come on top. It will either turn in to a scramble and some form of single or if you beat them on top you can force them in to a Leg Drag position.