Create username only


I'm using the Edublog theme. I have supporter plugin.

I would like to only allow visitors to create a username and not a blog.

I've tried different "Allow new registrations" options.

If I select "Only user account can be created", it still shows the "Gimme a blog!" option.

If I select "Only logged in users can create new blogs.", then I get a "You must first login, and then you can create a new blog." message on the signup page.

Am I missing something here?

I would only like supporters to be able to create blogs. Should I be using this URL,
wp-signup.php?supporter=1 for supporters to signup for a blog?