Group subscriptions are a limited resource. It wouldn't and shouldn't be -mine-. And many people already have threads in existing groups. (I suppose this argues for multiple-appearance threads.)
I think you are overcomplicating this a bit. Create a new group (you only belong to four yourself) or add some threads to an existing group. There is an existing group called Additional Writing Feedback. Do it there. If this means that much to all those involved, I'm sure you'll find a way to join the group. Most of the groups appear inactive anyway so it's not like you'll be missing a ton if someone has to drop one to join the feedback group.
http://www.thenextbigwriter.com/group-a … eedback-35
Rosie