I posted this question a while back and have since investigated the topic somewhat. Many vision improvement methods actually have drills where you attain photofocus. If you correctly do it, you relax your eyes into photofocus by shifting you point of vision beyond the book. 90% of eye improvment methods are focused on relaxation so this should help. The point is not to strain but relax into it, just as you are expected to relax your mind when photoreading. The mind cannot relax when the eyes are tense and vice versa.
