I've found where you can fall off to trigger the fight, but it's so finicky that I'm not sure whether pushing your squadmates off can trigger it (I suspect no). Once he becomes hostile, he should become killable using singularity and warp.
In any case, I teleported down there and killed him just to make sure that it doesn't break anything later. Everything goes more or less as normal until the second (now first) council visit. It tries to play both dialogues at the same time and locks up. Luckily, this glitch somehow lets you save during the dialogue before it locks up, and if you load that save and run back to Anderson, the scene plays as normal.
You are also able to skip both garrus and wrex. This might cause problems on virmire. If it does, we can just pick up garrus when leaving the citadel.
So, if a way to kill fist is found, it doesn't break anything too hard. All we need is that way to get a fist.
In any case, I teleported down there and killed him just to make sure that it doesn't break anything later. Everything goes more or less as normal until the second (now first) council visit. It tries to play both dialogues at the same time and locks up. Luckily, this glitch somehow lets you save during the dialogue before it locks up, and if you load that save and run back to Anderson, the scene plays as normal.
You are also able to skip both garrus and wrex. This might cause problems on virmire. If it does, we can just pick up garrus when leaving the citadel.
So, if a way to kill fist is found, it doesn't break anything too hard. All we need is that way to get a fist.