@reid not sure if they will take this on but you can pay the @administrators to get it done
Sorry, but no. 😦
The responsible code is quite strict about that:
Do you have a GitHub account? I would make it a feature request, but I can't say anything about its chances.
You'll want to listen to the hook I mentioned above, and make a call to groups.isMember() to check group membership status, and then save it to the corresponding users' information.