how much healthy fat is he eating? very important for skin issues.
i would suggest making sure he gets some fat like fresh ground flax seed, flax oil, fish oil, organic butter, and olive oil everyday.
also try rubbing some coconut oil on the feet, i think that will help. you could experiment with ways of doing this like rubbing lots of coconut on just before bed, then putting a baggie over the feet, and some socks over the baggie. this will allow his feet to soak in the oil all night long. i think that would help.