I actually got it to work shortly before you posted the smv, but you're right, it's nearly impossible to execute in real time. That's what I got my trusty snes9x for.
And when is that? As soon as the game gets back to the "normal" mode? That is what I'v been doing. It's not working.
What I did to find this out was pick a frame to press the button (hold for 2 frames) and if it didn't work, I'd try the frame either before or after. If you have a bit of patience, you'll eventually get it. That's how I find out the first possible frame to press a button in a TAS.