I seem to remember Matrox made something called DualHead2Go. To the computer it looked like a real wide-donkey monitor. It would simply split the input between 2 monitors. This is from a while ago so I don't know if they're still available...

OK, done a quick google:

Here's a link to the official site

Here's a Newegg Link

It's available in both VGA and DVI flavors...