Preventing VR mirroring to main display

I would like to add the option to run a VR game ONLY inside the Oculus Rift and prevent mirroring to the main display. Currently, I am setting the following in the Start() of my main behaviour:

 VRSettings.enabled = true;
 VRSettings.showDeviceView = false;
 VRSettings.loadedDevice = VRDeviceType.Oculus;

However it still mirrors to the main display.

Do I need to change these setting earlier in the loading sequence or is the problem caused by some other "Player Settings" value?

I am using Unity 5.2.1f1 with Oculus runtime 0.7.0.0.