It placed on a misc object that works like a poison in that the item is applied to the equipped weapon. Except that, instead of affecting it's next attack, it permanently adds the effect to the item as an enchantment.

Basically, I want to create something like Oblivion's Sigil Stones as a poison replacement.

Spells (and enchantments) can only be added to actors currently and there's no way to edit a weapon's properties. You'll have to wait for SKSE or go with an alternative approach.

Really? That stinks. I thought we already had add enchantment functions.