Still, I think it should at least be tried.
Here are some ideas I've had for the task. If anyone else has possibilities to contribute, please do so.

1) Zombie RohanKnight Swordmaster.
Pros: Lots of speed, lots of power, good HP, few restrictions.
Cons: Lousy stealth, atrocious saving throw, no way to deal with summoning/magic users, no reliable distance attack, no magic.
Odds: 50 to 1
2) Half-Ogre Haftedmaster (Worship Eru)
Pros: Good HP, can use divination/manathrust, can wield Grond in the Void.
Cons: Grond aggravates, bad stealth, Prayer is really expensive.
Odds: 40 to 1
3) Deathmold Possessor (Watcher in the Water)
Pros: Unparalleled attack power, good HP, great stealth
Cons: Can't seem to hit anything above level 100. Can't take the Watcher into the Void (there's a workaround for this, but it's ugly).
Odds: 25 to 1
4) Ent Loremaster possessing Ancalagon/Great Wyrm of Power
Pros: The wild card. Six Rings of Extra Attacks, Barehand Combat, a whole damn lot of HP, breath attacks, can summon Ancient Dragons.
Cons: Still lousy stealth, attack power is lacking, it won't be easy to get an Ent Loremaster to the point where he can kill GWoP.
Odds:25 to 1
5) Yeek Bard
Pros: It's a Yeek Bard!
Cons: Almost 100% chance of failure.
Odds: 8000 to 1
Those are my ideas. Anyone have comments?