This suggestion is more or less the same than this thread:
viewtopic.php?f=6&t=22640Keep in mind the split screen is already implemented: Menu->3D options->split screen.
The part that is not yet implemented is adding a barrel distortion to each camera. I'm not familiar with Google Cardboard, but the Oculus needs at least a barrel distortion in each one of the cameras like this:
(Actually, the oculus needs a slightly different barrel distortion for each one of the RGB channels)
Vik has already implemented distortion to one camera (
viewtopic.php?f=6&t=31058), and I'm quite sure the same idea can be used for Oculus/Google cardboard.
The headtracking part can be implemented using ideas similar to any other headtracking device:
http://wiki.flightgear.org/Head_tracking. Actually, I implemented headtracking with the Oculus in less than 15min years ago. My implementation does not work with the current generation of VR devices, but the idea is the same.