The good news: there is (a tool).
The bad news: I can't remember its name. Was looking for
about 30 minutes on google now, but can't for the life of
me find it. I found (compiled, and installed) one about
half a year ago (while I was working at a different job),
it was a tiny wee piece of C-code that came w/o makefiles
or anything, and I assigned keyboard-shortcuts that would
allow me to switch between the independent sessions running
under control of the same X11 server process.
I was running two independent fluxbox sessions on an
Sorry I can't actually help :/