In my Wilton classes, my teacher said I could use two tablespoons of meringue powder in a box cake mix to help stiffen it up for decorating. Meringue powder is just too expensive to be dumping into cakes like that. Has anyone ever tried using powdered egg whites in place of meringue powder? Or what about maybe just adding a few extra egg whites to the recipe? What are your recommendations for stiffening up a cake (mix or scratch)?

I've used the meringue powder in a boxed cake mix, and it does hold up better. My mother always added about 1/4 cup of AP flour.