My b2evolution Version: 2.x

-- Request for a plugin or a hack --

Hi guys, I need your professional help, I need a dark hack :)

I have some blogs and every blog has its group with the permission to write (only write) posts to this particular blog. Every new user should have the possibility to become a member of a special group (which will have the same name like its blog). The aim is, that new users can start writing post in one of these blogs with the help of the group permissions.
It would be great if somebody could write hack, that a new user can choose a group e.g. in a dropdown list during its registration process. Do you think it is possible?

Thanks a lot
Matt