...give items new properties? Ala the "Keen Edge" spell? Then "seal" the effects up using the crafting bug? The one that removes the last property you apply when spell duration expires. I experimented with the Magic Vestment spell, and substituted Negative Energy Protection as one of the effects, and the property "sealed up" just fine, but then I pulled my hair out trying to figure out what critters use level drain so I could test it. Then I tried using "Gaseous Form". That did not work at all, crafting proceeded like normal crafting. This is all because of those properties that weren't implemented, trying to find a way around that, but no spell duplicates what I want to fix anyway.
There are no level draining creatures in ToEE. The few creatures that do ability drain have had their abilities implemented through poison of all things. The only drain ability in the engine at all is a Banshee's Charisma drain, which works properly as far as I can tell, but wasn't implemented on any creatures.