IMC this - essentially just making up whatever the player feels like for his PC stats - would be a bootable offence.
For a kinder solution: The Raven Queen summons the Dvati to her side, taking him out of the campaign. The player gets to make another PC using actual 4e rules.
The best plan is usually not to handle this in-game, but rather to talk to the player out of game. Maybe he made a mistake, or maybe he thought you allowed it for some reason. Tell him to change to a normal race. If he's breaking the game for you and your players, that's not cool. But fixing it game will only lead to a big blow-up.
I can't quite boot him as I approved the character originally; however my understand if the character vs. the way its being played do not match. I'm making him bring me the actual dragon magazine and will go from there.
Just off the top of my head, though, there is probably a simple fix.
One mind in two bodies actually suggests the rules for summoned creatures should work well, here.
That is, he's got the two characters, but only one set of actions to do stuff with.
(Assuming you don't want to outright ban the character, which would be okay, too.)