Isn't there a vest of false life or something of this nature?
Anyways, if you want to you can have someone buff him up (if he has time) or have shield other on him.
Personally I like the max HP idea. That is what I do if I want to beef up an NPC without increasing HD. I guess alternatively you can dig through 3.0 sword and fist and use the toughness line - dwarf's, giant's, dragons toughness. I forget what hp each one gives but I think its something in the lines of 10 20 30 and you need the previous feat to obtain one after it. The prereqs I believe are a certain con score, but you're the dm you can just give him the feats.