How to estimate eye-in-head rotation (degrees of visual angle) from a 2D video of the eye?
In theory you can use the geometry of your setup to transform your data to the orientation reffered in the paper you mentioned using Scheimpflug Principle and then use the methods provided in it.
Practically, you can only approximate the geometry of your setup. If you have some idea about angles in something like this

please let me know, I might be able to do the math for you.
EDIT: The lens plane is parallel to image plane in cameras so now it is just the question of orientation of subject plane and lens plane(camera plane).