So I came across a nasty issue with the closed source nvidia drivers: if you enable TwinView through nvidia-settings, you automatically lose xrandr support:

Code:
$ xrandr -s 1
Failed to change the screen configuration!
This is something that supported pretty much universally outside of Nvidia drivers! Even fglrx has no problems with this. Now, this may not be that big of an issue for a regular desktop, but I'm developing a library that must support mode switching.

The recommended solution is to use the old XF86VidMode extension instead. However, before I go on and add a separate code path just for nvidia drivers that can't be bothered to support modern APIs, maybe there is a simpler workaround that can get XRandR to work on Nvidia w/ TwinView?

Any ideas?