Forgot Twitter password but no longer have that email account

Actually, it's a friend who set up a Twitter event for the gaming convention we're running, he can't remember what account he used to set it up, and when he tries to retrieve his password it doesn't show up on any of the email accounts he thought it was set to. We're trying to get ahold of the account so we can start making announcements through it. I need to let him know what he needs to do about it.