Interesting concept. I like!
Maybe your character can establish a link of communication with carrion eaters. Vultures, flesh beetles, worms, maggots, flies, etc. He might be able to commune with them (though I'm not sure how informative a conversation with a worm would be) or control them. The implications are disgusting, but maybe he could save somebody's gangrenous limb by compelling a horde of maggots to crawl in and eat out the dead flesh, but leave the living flesh untouched.
How about being able to concoct magical potions from certain molds or fungi that grow on dead bodies? Or from the petals of flowers left on tombstones for loved ones. The flowers themselves aren't anything special till they've been placed on the headstone; the act empowers or enriches them somehow.
Maybe he can take relatively fresh limbs and organs from dead bodies and transplant them into the living? If he can manipulate diseases, maybe he can remove the disease from a sick person and craft it into an immunization agent to administer to people? If he can manipulate dead tissue, perhaps he can preserve and craft dead flesh into garments (really nice fox pelt cloak) or disguises (wear the face/body of a dead person) or craft interesting weapons, shields, or armor from bone. Imagine a wicked looking suit of armor made from bones; the density of the bone has been increased dramatically, so that it rivals steel. Likewise he could make swords or shields. You could take that notion and run with it and have him craft some really interesting or useful devices from flesh or bone.
Of course there's always the novelty factor: So, Joe the Necromancer attends a boar roast and gets a little tipsy. He uses his control over dead flesh to reanimate the main course, and all a sudden this roasted boar jumps up and runs around the room, apple still stuffed in its mouth, causing hi jinks and more than a few fainting episodes.
