My advise, house rule it that an AOO provoking action doesn't provoke an AOO when used during an AOO.
I wouldn't do this for just this kind of situation:
So I sunder you, provoking an AOO, you use your AOO to sunder me... but by the house rule this won't provoke an AOO
This will stop all but the untrained from doing any of these cool combat actions. Most players are downright fearful of provoking an AOO (as well they should be) but there are a few special situations where your PCs will take one because they think that juice is worth the squeeze.
Ok this is probably a stupid example but...
Let's say that evil Dinglefairy the Drow is single handedly wiping the floor with the PCs thanks to his mighty staff of Coolness. Dwarfy McDwarfster desides he'll bit the bullet and sunder the staff in twain to stop Dinglefairy's reign of terror. He goes to do it and provokes the AOO (staffs [or is it staves?] are quarterstaff-like weapons), the drow replies by disarming him (with a two-handed weapon no less thus gaining a +4 bonus vs. Mcdwarfster's one-handed dwarven waraxe) and through a lucky roll Mcdwarfster's Axe clatters on the stone floor, and next round his brain is incinerated.
Dwarfy's player: "Thats BS, the drow shoulda provoked an AOO
DM: we houseruled that remember, it was too confusing, my aspirine bills were climbing..., but yeah and he only had 8 hps left too

Dwarfy's player: "what?! 8 HPs! I would've done that easy...if only..."[sobs

]
yeah, that was pretty lame. Just don't mess with the rules if you can help it.