First, glue the crack shut with super glue. Somebody makes such a glue for humans that you can ask for and buy in a drug store but it seems the same to me. Gluing the crack closed reduces pain way down. You will probably need to glue it several times until it heals. Ditto for cracks in fingers, corner of thumb, etc.
Second, use the Udderly smooth stuff from the first post or one of the other products to make the skin more pliable and healthy enough not to crack.
