Messed around quite a bit with swapping spells (trying to get an effect where i can make my warlock be in demon form all the time, but shut it off at will) and i never could figure out how to make a spell that doesn't normally modify the player model (ie Fel Armor) modify the player model.
As a solution, my request is for someone to do it the easy way, and swap the creature model for noggenfogger skelly to demon form. Might be a simple DBC edit, but I do remember getting size right to be a bit of a pain....