Interesting concept Mark !
I have two monitor outputs on my video card but I've never really thought of a use for the second one.
I expect you will have to wait for multiple viewports; then see if they can be partitioned across two monitors.
You might try and load GCP into two directories and see if you can launch them simultaneously.
The dongle may, or may not, have something to say about that but, assuming it did work, it could turn into a file-path nightmare if you tried to save from both copies.
Matrox, the maker of my video card, has some information on their website regarding dual monitor use. It definitely sounds possible to do what you want if you can get two copies of GCP running simultaneously.
You should be able to spread your desktop over the two monitors, have GCP running in two windows then just click on the window you want active...very much like running two windows on a single screen.
Or you may just find a unique way to corrupt your file system.
I think I'll wait for multiple viewports.
There's some interesting information on the subject at... http://www.matrox.com/mga/products/mill_g450/features_dh.cfm
If you get it working Mark, make sure you keep us posted.