Meetme special's configuration

i need some help. I have astlinux (Asterisk and meetme, all work well. And now, i need to do a specially configuration. I want that one user can speak in all conf rooms (700, 7001) of meetme when he enter in her room 799. Its means, if someone in enter in room 799, when he speaks, all users of others differents rooms hear him. But he don’t hear others rooms when the speak.
How can i do this?
I’m new in asterisk and meetme, so excuse me in advance for my questions.

Thank you everybody

I see this answer in other post (MeetMe Sip Client):
“Use a third conference and connect it to the other conferences using local channels.”

So, my file extensions.conf and call’s files are configured. This link was more helpful for me to know how do it:
In this link, it says we need to move call’s files to /var/spool/asterisk/outgoing.

I did and it works. But the problem is that, when Asterisk reboot all files in /var/spool/asterisk/outgoing delete. And the third conference can’t connect again in other conference.

I need that local channels work well also after a reboot.
How can i do to fix it?