You need to just hope for a reincarnation scroll to go on sale in the town's general store, unless you happen to have a druid in your group who can do it. If you can charm via scroll or spell and you run across an enemy druid, you may be able to get them to do it for you... But maybe only if you drop the corpse first. A tavern quest could do it too but it's unlikely... I think they can also show up as random pickups sometimes as well so search all floors completely.
If you have some unidentified scrolls that can't be identified, try using them on the corpse, then reloading from the previous save so you don't waste them.
You could let an enemy lightning spell zombify the corpse, or summon bones with a scroll if you don't have a necromancer in your party, but they won't last very long and can't be healed.
When reincarnating, don't save if it's not a good reincarnation, instead reload to get another, that way if it sucks you won't be stuck with a cave bat or dungeon creep or some crap LOL.