I realize it's a mechanic and not a rule, but 3.4.4 A. 5. says "Do not grant a time-out after a foul until the necessary information has been given to the scorer.
It's weak, but you could point to this as a reason to give the coach a chance to rescind his request. Since you shouldn't grant the TO until after you report the foul you've decided occurred before the timeout, you don't have to give it.
Now, the same mechanic also says not to grant a TO while the ball is in possession of neither team or the opposing team, interrupted dribble, etc, and we know if we do grant one it is granted.
So, like I say, weak argument. But use it if you like.
