I wanted to use my 20.1" Dell widescreen LCD in portrait mode while using my tablet in landscape mode to drive it. Toshiba's version of the nvidia drivers dont have NVRotate.
The solution is to extend the desktop to both displays and reverse the resolution of the external LCD i.e. 1050 * 1400, leading to Tablet Landscape and LCD Portrait.
On nvidia desktop gpu's, NVRotate is included so there's no need for the above.