Preheat oven to 350°F. Coat a 9x13-inch baking pan with canola cooking spray.
Add cake mix, egg, egg substitute, sour cream, water, and coconut extract to a large mixing bowl and beat for 2 minutes on medium speed. Scrape sides of bowl after a minute of mixing. Pour evenly into prepared baking dish and bake for 30 minutes, or until a toothpick inserted in cake comes out clean.
In a 4-cup measure, blend sauce ingredients until smooth.
When cake comes out of the oven, poke large holes evenly over the top with chopsticks or a barbecue fork. Pour milk mixture slowly over the top, so it soaks into the cake. Cover and refrigerate for a few hours or overnight.
Just before serving, spread light whipped topping over the top of cake and then sprinkle with the coconut.