Interesting concept. Seems like it would be best served by a chatroom of some sort. Tech-Forums had one in ages past, but it didn't see any activity. Since I don't IM (anymore), I'm not current on which ones have this capability.
Putting one's IM info in their profile could help facilitate this, as it would allow others to give them a shout and an invite. You can use the Who's Online link to see who is online and logged on (duh). You will find said link at the bottom of the main index.