Third Monitor for FCP6 on Powermac G5

I'm using FCP6 on a Powermac G5 Quad running Leopard. I now use two monitors, one for everything but the canvas, and the second montor for the canvas. I'd like to add a third, 1920 x 1080 monitor for using the Apple Cinema Desktop (or whatever it is called), but I of course only have two DVI outputs on one card. Can I use a third monitor and what would be the easiest way to accomplish it? Help is desparately requested.