How do I perform a ball push-up with 2-feet on a ball with a roll?

Begin in a push-up position with feet together on top of a ball and your hands on the floor, placed slightly wider than shoulder-width apart.  Maintain a straight line between your feet, hips and shoulders.  Draw-in your navel and contract your glutes.  With your back flat, slowly lower your body toward the floor, lowering and contracting your shoulder blades.  Push-up to your starting position being careful not to jut your head forward.  Hold the start position and roll the ball in by bringing your knees into your chest.  Extend your knees to roll back to the starting position.