Get DK2 Position Relative to Tracking Camera

How can you get the HMD position, relative to the DK2 tracking camera?
My goal is to map out a virtual space that will 'overlay' on the real world the same way, with each run...given that the tracking camera will never move.
A good demonstration of what I'm looking to achieve can be seen in Oculus' Demo Scene's "Tracking Bounds" option, that shows the camera's frustum, anchored to the world.

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Current environment:
Unity v5.2.1f1 Personal (64bit)...

Get DK2 Position Relative to Tracking Camera