Okay, some good news and some bad news:
The good news: I got Action Replay!
The bad news: It has zero functionality! That's right. Datel decided to remove code input functionality in versions 1.20 and later, even though it says on the box that you can input codes. Hmmm.
Nonetheless, I have figured out this dash/smash desynch completely. I don't have frame timing information, but I can tell it's a small window (1 - 3 frames).
In any case where Nana is on the ground and not sliding/running, you can dash/smash desynch by doing a dash attack in the opposite direction Popo is facing with a specific timing. So yes, you can do it from standing still. It's fairly difficult but after a little practice can be done consistently. It's easier, however, to do this desynch right after an attack. At least, it seems that way to me.
And of course, you can do this out of other desynchs, such as roll, grab, spot dodge, etc., but I'm finding it's more useful when done as a follow up to an attack. For instance, you're facing your opponent and hit him with an ftilt desynch (ftilt in both directions). Now Popo is facing away while Nana is facing your opponent. You can now do the dash/smash desynch into your opponent. Ideally the dash attack hits, popping them up for the smash attack to hit also.