This is a newer version of the virtual domain behavior I found on the
Radiant Wiki. This version is an extension designed for the current
“mental” branch and now no longer requires a patch to radiant to
work. (It includes a module into SiteController instead, which
should allow it to work even in instance mode.) Comments and bug
reports welcome.
http://silverinsanity.com/~benji/radiant/virtual_domain-1.1.tar.gz
~~ Brian