You can do this without pummeling, but it is very impractical (I tried this on marth and shulk and i manage to do it, but it was extremeley situational), pummelling will be a must for more consistency. Also, this does not work on big characters, or at least i could not pull it off on bowser nor DK, but i haven't tried it on DDD yet, Ganondorf can still fall for this though, and this will probably become little mac's biggest nightmare.
I tested this extensively vs. Little Mac earlier today. While grab fall to footstool works consistently on the bots, it's iffy on actual people, and I feel like most of the time it's either falcon that gets footstooled or neither of you. If you react, though, Falcon can recover safely from being footstooled in this situation as long as he didn't whiff his jump before hand, so the risk isn't too high.
On the other hand, I did discover something rather more useful- Falcon's grab seems to release at a different angle if they escape during a pummel. If you perform the grab fall technique without pummeling so that Falcon hits the edge of the stage through momentum without falling, and then begin to pummel once stationary; when Little Mac escapes the grab he will be released at a (I think?) semi-spike angle that he can recover from with his jump.
What makes this interesting is that it only gives Mac one possible recovery option, and I found that a well timed down-tilt on the very edge of the stage (where you should already be) will
always gimp that jump. After that, he can't do anything but fall to his death. This worked against real people as well, though I'm not certain if a more skilled mac could find a better escape from the situation. As it is now, I believe it might be a guaranteed kill so long as you nail the timing on the down tilt, which really isn't all that hard. This is a match-up specific trick, though- I'm pretty sure nobody else has a recovery so awful that this will work on them.
An observation I made that was more relevant to grab falling is that certain stages make it easier to do- I was hardly able to perform grab falls at all on omega boxing ring, but I was hardly able to avoid them on omega Mute City. Probably has something to do with the presence of the wall under the ledge.
Edit: I'd post video, but I have no way of capturing it right now. Apologies.