I've read through this whole thread, and it seems to me like you, or whoever in your group is the best at possibly really awkward confrontation, need to have a sit down with him and lay down the law. Generally I suggest the DM be the one to do this, because the GM can say "it's my game, it's being run the way I want to." The conversation is going to suck, he's going to get defensive, but you have to do it. Here are my suggestions:
His powergaming, and especially his cheating (and what he's doing IS cheating, even if it's only sort-of on purpose) is making the game not fun for everyone else. He needs to understand that NO MATTER WHAT that is unacceptable. Even if his builds are 100% legit and he roleplays incredibly, if it's making the game not fun for the other players, it's not allowed. No ifs, ands, or buts. That means that sometimes you can't play what you want to play, or play the game how you want to play. And that's just something you have to accept when you're playing with a group of people. The fun of everyone comes before what one person wants.
He needs to fully read and understand everything about his character, and the DM does as well. If he can't explain it to the DM while pointing out those rules in the book, he sits out the session until he figures it out.
If he gets caught cheating again, he is going to be immediately asked to sit out the session. He can play again next week (or however often you guys run). If he gets caught AGAIN, he finds another group to play with.
If he says that he's just making honest mistakes, tell him to stop playing such complicated characters. My rule for my players is that they get to use non-core material once they have demonstrated a very firm grasp of the core mechanics. If he can't keep track of the rules, he needs to play a ranger or a fighter or something else simple.
Start punishing death. If you want to be really hardcore, anytime someone rolls a replacement character have it be 1 level lower than the character that died. A less hardcore option would be to reduce starting gold by a cumulative 10% for each death. That will dis-incentive a cavalier attitude toward dying, but is pretty easily overcomeable if your new character sticks around. You don't need to direct it at him, just have the dm say "I want to make dying a bigger deal in the campaign. New rule."
Roleplaying issues are a lot harder to work with than rules issues. I have no issue being uncompromising about enforcing rules, but it's not really fair to tell someone who doesn't have the social skillset to roleplay that roleplaying is required. I like what other people have suggested: reward RP, but don't punish a lack of it. I have been absolutely amazed at the RP players will bust out when I start handing out XP rewards.
tl;dr a firm NO