Live Event Presenter Calling In, How to Un-Mute?

We regularly host live events for our all-team member meetings. One of our presenters is sometimes on the road and must use the dial-in number as a presenter (audio only of course).  It works great, but if someone mutes him within the live event interface, there is no way for us to un-mute him.  Is there a way that he can un-mute himself?  Possibly by pressing the pound (#) key or something?

To be clear, I am not talking about him muting or unmuting his own phone, I'm talking about un-muting in the teams live event interface.  In this last meeting he was muted by someone and eventually had to dial back in so he could speak, which was frustrating.