Can blog owners give author/etc rights to users in MS environment

There is a working WP3 multisite environment with multiple domain names (with domain mapping) and external authentication.
Everyone can (cross)log in and comment in every blog and that's fine. /every new user is a subscriber by default/
But when a new user record is created in the wordpress db it is assigned to a blog only.
How can the owner of the blog (with localadmin rights) give author/editor rights to someone in the network for his/her own blog?
Currently the blogowner can see only himself in the userlist of his blog, and the "add user" or "assign user to blog with specific rights" function is available only for the global siteadmin.

I hope I could explain it clearly :slight_smile:

Thank you.