It works like this: develop good impulsion and self-carriage in trot on a circle. Then counter flex to the outside of the circle and carry the shoulders toward toward the inside of the circle ("in"). When that is crisp ask for steps of haunches in (toward the outside of, or away from, the circle); this is like half pass around a circle. If/when Rijkens "falls" on his shoulder I again ask him to carry his shoulders in.
Key for me is absolutely insisting that Rijkens maintains energy and impulsion, thus maintaining through-ness and self-carriage on his part.
The gleam in my eye: