create /blog subsite on WordPress multisite

I have a 3.0.Best Answerite with MULTISITE enabled and would like one of the sites to live at /blog, but when I try to create a new site with that path, I get this error:

The following words are reserved for use by WordPress functions and cannot be used as blog names: page, comments, blog, files, feed

How can I get a site at /blog?

You can’t.

That’s part of the main site’s permalink structure. There’s no way to get around it. You can find more information here:

http://core.trac.wordpress.org/ticket/13527