How about something like this? It doesn't quite get after what I think you're after, but it's not too bad an alternative.
Reactive Parry
Prerequisites: Combat Expertise, Combat Reflexes, Improved Combat Expertise
Benefit: You can use the benefits of Combat Expertise even when it is not your turn (and even if you are surprised). If you are being attacked and wish to use these feats, you may do so. If your attack bonus is already lowered because you are already using these feats, you may increase your defense bonus, but not beyond your BAB. You may not decrease your defense bonus by using this feat (i.e. you cannot increase your defense against one opponent and then lower it against another in the same round). You may continue to increase your defense against subsequent opponents in the same round, but only to your maximum. If you are granted attacks of opportunity during the round, your attack bonus for each such attack could be different (albeit only progressively worse). After the last opponent has attacked you, even if you have not yet taken your turn, you must continue to fight at this adjusted attack bonus until your next turn.
Metagaming note: you cannot use this feat in immediate increments after the DM rolls for an opponent's attacks (i.e. Player: okay I increase my defense by 1; DM: he hits; player: okay I increase it by 2; DM: he hits; player: I increase it by 3, etc.). You must declare your intent before the DM rolls for a particular opponent.