I lie on my back with my feet up against a wall or couch, knees at a 90-degree angle. Then I cross one foot over the opposite knee to form a triangle, and gentle push against the crossed knee while pulling the foot towards me. Looks like this. This guy
works for me too.
It is a lot of stretching, but if I just grab a book and read it while using the other arm to push the stretch the time goes by fast.