Hi gain,
as far as I know: You can not
A Group does not have the same "level of features", as a User or a Company has.
I've played a bit with a new ObjectClass "WorkingGroups" to have the same features available as Users or Companies have, but it's a lot of work!!
And as long as there is no roadmap published, where I can estimate, whether my effort goes down the trash next version or not, I won't go further on.
cheers
markus