It doesn't take the feat away, he just can't use it while his dex is too low to qualify for the feat.
It sounds like you're handling him pretty well, actually. I have a player who has similarly optimized characters. The problem here is that his character is so much more powerful then the other characters. The solution for me has been to beef up the encounters a little and throw the tougher stuff at him.
The other behavior he has is wanting to play nonstandard character races and such. Orcs and tieflings. I've found that it works well for me to encourage the roleplaying aspect of it and use the ELC rules and the addendums to them in Unearthed Arcana. Basically, if he wants to play something wierd I try to allow it if he can come up with a good roleplaying explanation.
The combination of these techniques has turned this particular player from a minmaxing powergamer into one of the biggest contributors to storytelling in the group. The crux of it has been to try to find ways to say yes to him, while standing firm on stuff that I feel is unbalancing.