I'd be interested in this too - I was playing games with friends for hours on Friday and this was a slight aggravation, especially if we were having a rematch. It was also slightly tricky when trying to coordinate with friends about what games to play especially as most of them were fairly new to the site.
Something we tried using was putting all the friends in to a group, and then using a group chat (Discuss option at the top right of the group screen), but that seemed a bit inconsistent about whether people got the message updates. It also lacked the option to do a voice/video chat with the group. My ideal set up would be to have a private lobby within BGA as a way to keep my friends in games with each other if it's that kind of occasion (Friday was my birthday, so I was using BGA as a way to just hang out with friends whilst playing a few games). I'd hopefully then have the ability to switch between a 'lobby/group' chat and the game specific chat so it would feel like hanging out in a room with friends.
At the moment, if I do something like that in future, I might look at using something like Discuss/Whatsapp to have as the group chat, but it would be nice to keep it within BGA
