Since we wont kill with WoP anymore, i was trying to figure if there was another way to melee a mob to death without damage...

Negative levels.

Now, is there a build possible to use that method?

There is 2 ways to inflict negative levels with a melee weapon:
1- Shroud Enervation weapon (neg-Fire)
2- Dreamsplitter.

Now, the Greensteel weapons proc at a rate of 5%. A 5% chance to give 1d4 neg levels is just not as strong as Vorpals, who kill 5% of the time. Even dual-wielding, Vorpal still wins.

Let's check out Dreamplitter. Now, the splitter also as a 5% rate, but it can be increased to 10% with imp critic Blunt. A Kensai 3 fighter will even be able to get it to 15% (18-20 roll).
Still rather weak considering the weapon type.

The best i could think of was:
Fighter Kensai 3, with improved crit, a dreamsplitter, and Stunning Blow to get auto-crit.

Anyone as a better idea?
Or is it just a lost cause?