Change primary domain to a subdomain

I run a network, configured with subfolders (not subdomains) and using domain mapping on the sub-sites. I want to use the primary domain for something else, but I, of course, need to maintain the primary site for administration. Can I move it to a subdomain on the primary domain?

For instance, can this…

mydomain.com <- network primary site
subsite1.com (folder subsite, domain mapped)
subsite2.com (folder subsite, domain mapped)
etc.

Become this…?

wp.mydomain.com <- network primary site
subsite1.com (folder subsite, domain mapped)
subsite2.com (folder subsite, domain mapped)
etc.

I feel that this should be possible. Am I wrong?