In Fedora 18, I could use
gdmflexiserver to start up a new instance of X and GDM on a new VT. In Fedora 19,
gdmflexiserver appears to have lost the ability to do this, and I'm looking for its replacement.
By Fedora 22, it's not necessary to spin up a new instance of GDM to log in a second time, as user sessions run on a separate VT. In the default configuration, VT-1 holds GDM, and the first user session is on VT-2.