The first of my theories comes from what we've already seen from the season before WAT and The Firebending masters
The Awakening, during Aang's healing secession
Aang: Wow, you are definitely in the right area there. Katara: I can feel a lot of energy twisted up around there. Let me just see if I can...
Which leads to my first theory, that since we know Zuko can redirect lightning, and that the Aang's wound contains energy, that it might be possible for Zuko or Iroh, the two firebenders who are more so versed in the redirection of energy, might possibly be able to somehow bypass the hole and return the Avatar state to Aang
If it wouldn't be a permanent solution, perhaps Zuko could teach Aang to redirect the flow of energy in his own body. Which brings me to the second of my theories
We know from the Firebending masters that fire isn't just destruction but energy and life.
Seeing what the full moon can do for waterbenders and Bloodbending, could that mean that there could be some sort of firebending alternative, where the comet could power up a firebender and allow him or her to control the energy of a person, thus rendering them harmless (much like bloodbending)
This could prove providential for Aang if it would become a necessity to defeat Ozai on the day that Sozin's comet returned (Imagine if there was a full moon that night.)
Interesting. I like it. It's very possible. My two things against it is that there's what, 10 or so episodes left? I don't think the creators could start a whole new branch of things, unless they did it very briefly. Also, that sort of...energy/power/aura seems a bit extreme for ATLA.
But I still like it. And it would be awesome if it could happen!