[Shardphoenix]

Chalice, chalice... Be more creative, guys, seriously. Gift of Health (a global spell) is much easier to get if you have some nature magic. And if not - almost every tribal shaman has at least N1.
I don`t think that pretenders die from disease (AFAIK, they just stop at 1 hp), but i`m not 100% sure about it.
Other variant is casting Twiceborn on your pretender and getting killed (not drowned) in friendly dominion. He will return as undead wight mage with immunity to disease (still can get diseased, but no HP loss or afflictions) - i used this trick in SP to get boots slot on my archmage, so i`m 100% sure that Twiceborn works on gods. You`ll need at least 2D on pretender, or 1D + a skull staff, however.
Casting regeneration on him in combat is another way of keeping him alive for now - in combat, regeneration still restores your health to full.