As far as I've seen, you list 'cake mix' (baking mix, or whatever you're using) and in parenthesis, list those ingredients. After that, list the rest of your ingredients.
Example: baking mix (flour, sugar, baking powder, salt, etc.), sour cream, egg, vanilla, etc.
I'm in California, and that is acceptable according to my health department. It would be best to check with your own, to cover your bases.