So I kinda made a big discovery. It involves 2 things.
1. There are two frames of ledge snap vulnerability.
2. When you hold down while offstage flame choking toward the ledge, you don't immediately grab the ledge (release down to grab ledge).
So you can cover the ledge by keeping the flame choke hitbox out. (Remember aerial flamechoke's hitboxes are active frames 19-31) Teleport recoveries to the ledge are actually edgeguardable as long as you read/react to the startup of your opponent's recovery. The idea started as theorycraft, but then I tested it in training mode on Sheik and Palutena and it works, and used it in an online Anther's Ladder match against a Sonic. I'm going to assume it works on other teleporters (Zelda, Mewtwo) and covers ledge on low recoveries without dangerous hitboxes (Robin, Pit/DPit, Dedede, Olimar, Villager, Megaman, ROB, Greninja, DHD, BowJow, Rosaluma).