Is there a way to put already registered user in a group?

Hi SI Team

I have read this here:

http://stackideas.com/docs/easysocial/administrators/groups/auto-join-groups

But am still lost…

I have a site with nearly 800 members and would like to put them in a Group.
They have already registered.
Is it possible to do this?
The only way I have found so far is going to ES Groups/Members in the preferences and adding them 20 at a time…
I am trying to get all members into this group here "BUG Mother Ship"

thanks

Paul