T.D.
Have you considered looking into donor breastmilk instead of formula? Have you tried the different "tricks" to help you pump more? Here is a link to an article from kellymom.com that you may find helpful. http://www.kellymom.com/bf/pumping/pumping_decrease.html
Also, you will need to pump while you are at work to keep your supply up so you may find you actually need less formula than you think.