Simply have a point on your legs page that you will not fly over. Runway center line at 10 miles for example, this point is then alway the active waypoint and if you do not fly close to it the legs page does not sequence. Dont put an approach in as you are doing a circuit by looking out the window so it is not needed.
As for the power setting we use 88% which approx. climb thrust for a B733, and our circuit rules are no automatics so manual thrust.