Ah okay. Would this be considered a feature request for an upcoming version of GJ or is it something that would require me to hire someone to do it for me? I'd do it myself but I'm 90 percent designer and only 10 percent developer.
You can request it in the GroupJive Forum, but it would be faster if you hired someone capable of doing this for you. If you'd like, you could then share it with the rest of the users here on JP.
All the logic is in the current GJ CB plugin. It would be fairly simple to create a new plugin with one parameter called "Group to add new user upon registration". Guessing 3 - 5 hours worth of work. I would do it for around $100