Protected threads

[tehtide]

Ok... so I have a need to create a forum that is hidden from all users except for a specific usergroup. That is no problem... but what I need to add if it is possible is a way for someone in that user group to "invite" another user into a thread in that forum and allow them to read and respond to posts.

Basically we need to have a protected area where a select few can post and view, but then the ability to change the permissions on a single thread in the forum to include another user that isn't in that usergroup.

If there is something like that already could someone point me in the correct direction?

BTW... we are using vBulletin 3.6.8

thanks in advance!!!