C.M.
I would honestly just try to feed him 2x a day - with 1-2 tsp of cereal and mix it with formula or water. Do not worry about EXACTLY how much and don't count the formula towards his total amount he's drinking (I never did). If he's still drinking 35 ounces of formula, I"d say up the amount of cereal. Maybe he's just hungry! I started my son on cereal at 4.5 months because he was hungry all the time! Good luck!