I don't think so, but here is a thought. Go to <ctrl>+<alt>+F1, log in as a different user and startx. Then you switch back and fourth using <ctrl>+<alt>+Fn...
I have never tried this, but it makes sense to me!
The error specifies that the server is running on Display 0. I'm guessing there must be a way to start it on another display, say 1! I'm curious so I'm gonna try and read up on this too. Let us know if you find a solution on your own!