Preheat oven to 350. Prepare a 13" x 9" pan with cooking spray and flour; set aside. In a mixing bowl, combine three cups cake mix, pumpkin pie mix, eggs, oil, and pumpkin pie spice. Mix until well blended. Spread into prepared pan. In another mixing bowl, combine remaining cake mix, coconut and walnuts. Cut in margarine with pastry blender. Mix until crumbly. Sprinkle over moistened cake batter. Bake for 35 minutes.