To-die-for Red Velvet Cake

I kid you not, this is one of the best red velvet cakes I have ever made. It's easy, extremely semi-homemade, and really diet-friendly, but you'd never know it by the taste.

Cake:
1 package Duncan Hines Red Velvet Cake (I avoid Betty Crocker like the plague)
1/3 cup egg whites from a carton
1 can Diet 7-Up
Pam with Flour baking spray

Frosting:
1 container Pillsbury Whipped Cream Cheese Frosting
Equal amount FF, SF Cool-Whip

Directions:
Spray Prepare cake according to package directions, substituting egg whites and 7-Up for oil and regular eggs. Spray 12x9 baking dish with spray, and bake per package directions, adjusting for your oven. Allow cake to cool, then frost with blended frosting/Cool-Whip mixture. Store in refrigerator!