Unity5.6 + SteamVR: Disable native VR support and back to use SteamVR plugin

Hi, anyone knows how to disable native VR support and still use SteamVR plugin to control the camera? I wanna use SteamVR_TrackedObject.cs to control the camera as how it worked in Unity5.3. Mannnnnnny Thanks!

More details:
I’m working on a project which only use 1 Lighthouse, and put the VIVE Tracker on the back of head as a backup tracking to support 360 degree tracking.
In Unity 5.3, the positional tracking of head was provided by SteamVR_TrackedObject.cs, so that I can use this script to control an empty object, and set the camera parent to this object. When HMD not facing to the Lighthouse (maybe angle > 90 degree), I’ll set the camera parent to the VIVE Tracker to avoid bad tracking.
However it doesn’t work in Unity 5.6 because of the native VR support. The camera is controlled by Unity directly, so I’m wondering is there anyway to disable native VR?

OR if anyone has a better solution under native VR support, please help, thank you!