Extend display over network on linux with VNC
I think your best bet is Xdmx. Note that it is possible to run an X server on a Windows machine. Cygwin has an X server, and there are others.
But as far as I can see, Xdmx doesn't require the two X servers be on different machines. Just run a normal X server on display :0, Xvnc on display :1, and then use Xdmx on display :2 to multiplex them together.
It should be possible to script this so you don't have to start everything manually, but you'll probably have to write the script yourself, because I've never heard of anybody else trying this.