I am sure it is possible, since the video card outputs to the monitor, the cable and monitor is a bit different but same concept and same program, its only a matter of outputing different data to the video card from... perhaps USB?
I know it is not standard and I do not really need this just thought it would be interesting to do that and I could have an extra monitor, though it might require a custom program or be complicated to accomplish, just thought Id ask if someone has done this or not...
Either way, yes I do have a video card with 2 outputs, but I just might buy another monitor when I have money for it...