Lol, wow. This thread has been revived twice!!! Now it's 6 years old!!
I highly doubt nvidia will ever make it so you can span across SLI to span 4 monitors....sure that might be great for the 10 people who would use it. It's just not worth their time.
Here's an idea. Get a triplehead2Go thinger, and attach another one to each of the three spots. Now you have a 9 monitor span!!! (I wonder if that would actually work...) Other than of course your video card grinding to a halt from outputting 17280x1200
9 24" widescreens FTW!!!!