After selecting any star except "Big Bob-omb on the summit", enter the cannon next to you at the start and aim it as high and as far to the right as possible. Keep trying this until you die in the air but with your feet on the wall of the level. You can also make it look like your whole body is on the wall by going to the second cannon in the course. To do this, aim the highest and most further right as possible and fire. Repeat to eventually die on the ground but it will appear as though you were on the wall before the camera finds its proper angle.