In MS, how do I move the primary site to a subdomain?

I had a single install of WordPress with my theme, content, etc. I converted my install of WordPress to a MS install in prep for more sites, WordPress made my former single-install-site the primary site (ie if you go to example.com you go to this site). I have another subdomain site setup too (site2.example.com).

Is there a way that I can make the first site a subdomain site and make a new landing page for the baseurl?

So there are two sites: site1, site2 and one domain: example.com

Right now my structure is: site2.example.com and example.com (which is the theme/content for site1). I want to get to: site1.examples.com, sites2.example.com and example.com (which will be a frontpage for the blog network)

Any advice?