Ah, excellent, I missed Bolstering Blood completely. Orcus is Gargantuan, so if we push him diagonally, he leaves 7 squares each time, dealing an average of 7*14.5 damage to him. Now, we only need to push him 15 squares to kill him. That should be doable by a Lvl30 Wizard...
Tiefling Wizard/cleric/Blood Mage/Demigod
Starting: 8 Str 10 Con 11 Dex 18 Int 13 Wis 18 Cha
30th: notably 28 Int 28 Cha
Req feats: Initiate of the Faith, Novice Training (Cause Fear)
Nice Feats: Hellfire Blood
Trick:
Bolstering Blood on a Blood Pulse, targetting Orcus
AP for Cause Fear
Cause Fear makes him move his movement + cha mod away from you, or (6+9) 15 squares. He also avoids "unsafe squares" and difficult terrain while doing so, and as it must be away from you, controlling his direction of travel should be plausible.
(if it isn't enough the first round he's 15+ squares away and movement is painful, and you can Soul Burn to get Cause Fear back, triggering the same Blood Pulse again for another 15 squares. There isn't really anything Orcus can do against you at that kind of range, and he can't afford to move into range because it would kill him, even assuming you were a mere 15 squares away).