Literally everything has to be done to the frame. We have been trying to get an infinite, or some kind of extended combo using his roll for a very long time on and off, I am so glad ded_ found this.
Basically you have to perform each piece to the frame. You have to release the ball the instant he recovers from the pop up, meaning, the first frame he starts to roll should be the last frame he holds his uppercut, so you actually see that whole frame move sideways for one tick, and then the instant you land you need to jump, and hit the JPS as soon as you leave the ground. Flawless timing.