I find myself doing this a lot of times, and it works kind of well. I have not tested this extensively or anything but my brother and friends usually play with... Link, Toon Link, Falco, Fox, R.O.B., etc.
For the most part when edguarding and you throw someone off to the side, and they end up grabbing the ledge, a good tactic I like to use is standing right next to him on the ledge, but not DIRECTLY next to him, a few steps back, facing him. If he hits the attack button, (unless the knockback is too great, again, haven't tested it) you should be able to quickly do a down grab which sends him right back to grabbing the ledge. You can keep repeating this.
Stand near the ledge, down grab, he catches the ledge again, hits attack, down grab.
Of course, he has to attack. But the neat part is if he jumps you can always try to b-air or u-air quickly too, which usually hits, as long as you are prepared. Just have to watch out with Toon Link and such character's d-air. Although I have managed to pull off reflectors in time for that too which leads to some nice moves you can show off.
Hope it helps.
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