delericho
Legend
The current DM keeps trying to talk to me about ways to kill the PC off, but then keeps backing off because he knows that's very bad practice.
Yep. You have an out-of-game problem. In-game solutions are inappropriate.
We currently have such a "problem child", a character that was built using several disallowed sources, and equipped almost entirely from a disallowed source.
That character should have been banned as soon as it appeared. Given that it was not, I see two choices: (1) suck it up, or (2) tell the player the character is causing too many problems and he'll have to be removed. In the latter case, you may well lose the player; you may or may not find that an acceptable sacrifice.
Because of the people involved, and because of the multi-DM nature of our campaign, I don't see our own situation as actually being resolvable. No single DM really feels comfortable laying the smackdown on him, and if we have a group vote it will look like we're ganging up on him.
The multi-DM nature of your campaign actually gives you an out. Because of that, your list of "disallowed sources" doesn't really have an exception for "DM's discretion" - every DM would need to agree to make the exception, and presumably that didn't happen?
So, have the various DMs get together to discuss the situation. Then, they should meet with the player collectively, say that there was a mistake made (DM X shouldn't have let the character in without consultation), say that they've been trying to make it work, but that they've now decided that it just doesn't, and say that his character will just need to be retired.
Of course, that relies on the DM who first allowed the character agreeing to take the blame for the error...