embed + groups (VB 3.5 integration)

I've been working on improving the integration with Vbulletin and have gotten most of the way there in adding improvements. The previous implementation was a start, but it wasn't really robust. I've gotten the following previously missing features working:

1. Updates to the VB user (whether done by the user or admin) gets updated in Gallery. Things such as email, etc.

2. Added support for first and last names (from custom profile fields in VB) to be mapped into gallery. Previously was just the username.

3. Much easier configuration....all config variables are at the top.

4. One switch turning on of debug mode...so that you can have errors output or not.

5. Support for primary group mapping from VB to Gallery. This includes automatic creation of a gallery group to reflect a group in VB if it doesn't exist already, adding members to a group in Gallery when they're added in VB.

This is where my issues come in. To make things easier, as a first step I'm only supporting the primary user group in vb. My thinking is to handle this I will (its kinda hacky):

a) remove a user from any gruops they belong to in gallery and then
b) add them back into a group in gallery

I'm good with b), but having a tough time with a). I could go through all groups and remove them but I can't figure out how to do this. Ideally I would like to find out what groups they're a member of and remove them from those (so I'm not going through all groups).

I just can't figure this out. I'm good with checking externalIDmaps of groups, users, etc....and removing them. But this is beyond my knowledge. Seems as though there is more functionality for users than groups but I may be missing something.

Any suggestions for accomplishing a)?