Did anyone manage to enable the dual monitor mode?
I tried starting the game as a normal user and as admin. But in the options menu I dont have any available resolutions to choose from. Manually editing the game options .txt file doesn't help either.

Both Screens have the same resolution.

It's necessary to run the game in DirectX 10. But it's not easy to run the game in DirectX 10 on newer machines. If you enable DirectX 10 it will crash in the menu. The only solution I found was to uninstall the optional Windows update kb2670838. After uninstalling the Windows update you can start the game and enable DirectX 10 and Dual Monitor mode.

Edit: This was tested on Windows 7.