How should I do this spell? (Custom Spell / Trigger)

Ok so all Im trying to do is have a skill that every 15 seconds generates 2 corpses near the unit.. (note: its a passive unit skill (so no hero points need to be put into it))

I could do triggers but it might get really laggy and I used the "Create Corpse (undead)" from the graveyard as a base and made a skill that does nothing but has an icon just to represent the Create Corpse but It doesnt work. It used to when I didnt have the skill that did nothing.....

So all in all, should I stick with "Create Corpse" and an Idle Skill, trigger (needs to be so 12 ppl can use this hero), or have you give me a base skill idea?

The unit is a hero that has this skill, but needs it as a passuve type thing (Some hero skills will need corpses nearby to function, and this will make sure there always is).

Check out the Graveyard building, i think it has an ability wich lets it create corpses. I guess you can edit the ability so U can choose what unit type is used for the corpse. But I'm not sure about it

I already tried that.... It works but it seemed to stop when I added an Idle skill with only an icon, but no effect.