If you have him in a tank change it out for a reptile cage (I use Reptile Basics cages) or a tub. This will really be an easy way to deal with lack of humidity
I live in the high desert of central Oregon and our humidity is really low. My rack system and all of my reptile cages hold the humidity really well. When the snakes go into blue, I throw in a little long fiber sphagnum moss and its all okay again!!