[GearVR.Settings] HeadModelScale=0 kills the head motion but also the eye stereo disparity and because of this the stereo effect.
This is not a workable solution in my case. There is almost no point in a GearVR VR app without stereo rendering.
I still need a solution for locking or disabling the head motion. I can’t remove it myself by substracting the head position back because I can’t get the actual position on GearVR with with “Get Orientation and Position”. It always output 0,0,0 for position.