feed him more often. don't let anyone tell you differently.
once a week is a maintenance feed cycle for adults, not juveniles.
ask the same on a real king snake board, like kingsnake.com and you'll get the same answer. or join colubrid crazy on facebook: https://www.facebook.com/groups/ColubridCrazy/ you'll be able to easily interact with some of the most well known and respected lampropeltis keepers on either board.