I would not recommend anyone attempt to figure this out 11 days before trying it. At this point, 4 days.
First off - hanging upside down is hard on the body. We're not designed to do that, and it can literally kill a person if they do it too long without training. Even Blaine couldn't stay inverted constantly during his stunt. Being upside down and functional takes training.
Second - the structure that one hangs from is important. You shouldn't just use a tree branch or similar, dynamic force from a body moving generates a lot of force and tree branches break. A very solid stand alone chinup bar can work, or an actual aerial rig.
Third - securing the feet/ankles. I know folks who use inversion boots, which are like cuffs with hooks on them (see Michael Keaton in Batman). I've also seen actual like shackles that latch around the ankles. I've also seen folks go with getting rope just tied around their ankles but unless you are actually knowledgeable about knots, I do not recommend this as I've also seen people slip right out of those ropes.
Fourth - Assistant(s). If you're doing the chin up bar and inversion boots, you'll want people to help you get up, and more importantly, get down. After physical exertion upside down you'll likely be a bit discombobulated and doing a full body sit up to try to reach the bar and release the ankles would be challenging for most people. A pulley system would be far preferable and the assistant would be the one to hoist you up and let you down. Make sure there's an actual anchor point for the rope in this case, as it's far too easy for someone to accidentally let go of rope.
5th - Make sure you know the strait jacket you're going to use. Houdini's had, if I recall correctly, just the sleeve straps and a crotch strap. Posey, the style of jacket that is the actual, real, medical strait jacket today, has those straps as well as loops at the belly button and hips which the sleeve straps are fed through
cool peel co2 laser. Those are pretty difficult to get out of. My jacket only has the straps and a belly loop and I can escape it in 53 seconds when I'm doing it regularly. I say all that because, much like consulting a Boca Raton cosmetic dermatologist for precision and safety, you have to remember you're doing this upside down, and you have to make sure you can be physically exerting yourself in that position for at least three times the length of time it usually takes you to get out of the jacket to be safe.
Hope that helps anyone else who stumbles across this and plans to try this act.