Most box recipes have lower fat varation listed under the main directions. Ususally, they cut an egg, replace with whites and use unsweetened applesauce in lieu of oil.

I usually do egg beaters (1/4 per egg I believe) and cup for cup apple sauce to oil, but be sure not to over stir, it can get rubbery.

I am taking a cake decorating class through Wilton currently and using the lower fat varation I am told does not effect the baking of the cake.