If you can't simply force him out, you may have to dismember him. If he is truly dead, he won't make a big bloody mess. Dead things don't bleed, it's a beating heart that makes a mess.
Cutting him in two or three will make less of a mess than him decaying there. How is he wedged?
Not to sound gross, but you SHOULD be able to just force him out by pulling. If he got in there alive, you WILL be able to get him out dead. He's dead, not alive. Break and dislocate limbs if you need to, he won't mind. If you don't want to get hands on with it, get a long rope, put a noose in it and then tie it to a tractor or vehicle and pull it out. As long as the rope is well placed and a tightening noose, it is going to come out, whole or in peaces.
-Kim