you might want to try ULTRA KID CARE by Metagenics. it is a rice formula - non-allergenic. i am using it while i return to work because pumping stinks for me too. i get it from my chiropractor. it is a really high quality, pure meal replacement powder so you cannot find it at a pharmacy or GNC type of place
also, i wouldn't recommend soy formula as it is 98% corn syrup (same ingredient in candy!). also, goat's milk is the most similiar in make-up to breast milk. you can do 1/3 goats milk, 1/3 carrot juice, and 1/3 water combo and it's like mama's milk. are you in california? you can get great raw carrot juice from trader joes and the goat's milk or try whole foods or another health food store. if you aren't near trader joe's you might want to get a juicer and make your own carrot juice (see if he likes it first) because it can be pricey - but get raw !! so that it has the nutrients
sorry, keep thinking of more stuff - another thing to try is Ultra Flora form Metagenics or Probio Defense from Xymogen - these are high quality forms of acidopholus (the healthy bacteria in yogurt that aids in digestion and other areas of the digestive system) formulas are difficult for their new tummies to deal with and this could help. breast is best though =)