How to allow self-registration to join a specific Wordpress MU blog

I have a Wordpress MU instance installed.

I allow self-registration, and self-creation of blogs.

I have a user who has created a blog for a Chemistry class. He wants his 100 students to be able to self-register and become authors on this blog.

By default, when you follow the Wo开发者_JS百科rdpress MU register link, you are signing up for a site-wide account not for this specific blog.

How do I do this? It would be very painful to have to add the 100 students one by one as the administrator. Besides that, we don't actually have a list of the 100 email addresses.

I need a way that people can either request to become part of the blog, or automatically start contributing right away.

Try asking in the BudyPress forums, BudyPress is a social networking plugin for MU. (It might actually be closer to what your looking for)

What I'm doing is hiding registration on the main site and forwarding them to first find their blog and then register on the blog's website for the group for them to join.

In Settings->General why not use the option that lets anyone register. Then the students can each provide their email?

Then what about the Tools->Import->WordPress facility? First do Tools->Export and look at how the file is structured, then create your own XML file with just your users, then do the Tools->Import->WordPress thing.