Nvidia multi-monitor setup won't span screens

I have an Nvidia GTX 680 with multiple screens using twinview. Works great for general use. When I try using Wine, the window is never larger than a single screen, even if I set it larger with winecfg. Also, programs that use full-screen will also use only one monitor, while the other goes black. How do I make these programs truly think that my monitors are one giant screen?

Oddly, most of my web searching has found people with the opposite problem - their windows always span the screens.

Xrandr reports that the screen is 5760x1080 (for three 1920x1080 monitors).