is there a way of my mixing something else into their diet which contains no protein to balance the high with the low?? or is that just a stupid question

I can get free loafs of bread everyday from work, what if i always threw in bread with the purina daily?

I feel bad rejecting the order of the purina, the warehouse is going out their way for it, maybe they can cancel it if I call early tomoro morning, but then I still need another rodent food