my daughter had the same problems. i used the light karo syrup. excuse me for my frankness, but i don't know how else to describe it.....Karo syrup will only "lube" the poop - so it will still be hard. prunes will soften the poop. use the what you have to go get over this "attack" but once this spell is over, use the prunes to keep him regular.
for the karo syrup - i think i twas 1tbp for every 3oz of formula and put it right in the bottle. you can do this in every bottle until the "attack" is over.
i used prune juice - in 1 bottle a day i would put 1/2 oz of prune juice to keep her regular. if i saw her starting to get constipated i would up it to 1oz.
if you are using rice cereal switch to either oatmeal or barley it's less binding.
avoid all the baby food w/ bananas (alot of the level 2 fruits are mixed with bananans etc).
once my daughter turned 1 and was eating more regular food (not baby food) and was off formula and onto whole milk i didn't need to use the prune juice anymore.
i still need to watch her consumption of bananas & cheese (of course they are her favorite) but i counter act them with rasins or grapes to keep her regular.