Activate Parasite

So, I've been having some.. issues with the Parasite ability: First of all, I am trying to tell a unit to 'activate' the auto casting on it. I've done this with numerous other abilities (Cold arrows, fairie fire, etc). The problem is that "Neutral - Parasite - Activate" Or some such, doesn't appear in the "Issue an order to a unit without a target" like the others do. Also, I don't seem to be able to set parasite as even a default active ability.

More info: I'm not actually using parasite itself, but an ability based off of Parasite (The naga version). I'm pretty sure I could crack open the trigger editor and insert 'parasiteon' or some such, but I'd like to know if there's a normal way to do this in the editor I simply over looked... perhaps there's a trick in setting active abilities I'm not aware of?

Problem solved... I swear I just tried that map and parasite wasn't being cast, and then posted this, and tried again and it was. Sometimes I think I'm fixing my problems behind my back without knowing it.

how did you ever get it to work, I'm making spell based of of parasite, and I cant get a unit to turn auto-cast on using a trigger.

How do I do it?