There's no way to do what you wish to do in 6.3.
In 6.7, which you should really upgrade to, you can decline him from the queue, and not send out a mail using an option at the bottom.
Perhaps you can just edit his email address to be nonexistant, decline him, then edit his email address back? That way the mail would go nowhere.
_________________________
What do you mean "You're the bomb, run away?"