You say you "know that you can sli and get 3 screens" but that isn't true... if you SLi you can only use one of the outputs on those cards! It's an unfortunate SLi limitation that hopefully nvidia will fix one day.
There's a free program called SoftTH you can try. You'd have to have at least 2 non-SLi'd graphics cards (but one of them can be cheapo like the 8400GS).
http://www.kegetys.net/SoftTH/
Someone got WoW running at 5760x1200.
[url]http://www.kegetys.net/forum]
Note that switching between TH2Go and SoftTH usually means moving your monitor cables around.