Preheat oven to 350 degrees F. In a large bowl, combine the following ingredients until smooth: cake mix, margarine, sour cream and egg substitute. Spray 9x13 inch pan with non-stick cooking spray. Press batter into bottom of pan; set aside. In a smaller bowl, add powdered sugar, cream cheese, egg substitute and vanilla and beat until well blended. Pour filling on top of batter. Bake for approximately 25-30 minutes. Serve warm or cold.