Private Threads for Groups

I don't know if this is possible or not, but it would be really handy if groups could make some or all of their threads private. Right now, my clan relies on private messages for clan chatter. We had our own forum briefly, but staying on top of two KAG forums seemed a little silly. A private mini-forum in our group would be much more organized and easier to manage than conversations. It would also give groups more of a purpose.

 

As great as his would be, I'm pretty sure it's not possible within the group add-on the forum uses.
I believe we use this one: http://xenforo.com/community/resources/social-groups-for-xenforo.267/
But who knows it may be possible with some messing around with more add-ons/code.