Invisible summoned units

Ok, here's the deal... I have this hero that summons units that have, say, a special attack. But I want the summoned unit to be invisible to give the impression that the hero is the one that has the attack...

I was able to remove the shadow of the summoned unit, but I can't make it invisible totally.

I'm thinking you could do something like this in triggers:

Hero-Summoned Unit, Make Summoned Unit invisible...

But is there a better way that is not trigger-based? I want to use triggers only as a last resort...

Thanks!

Change the Summoned Unit-Type´s Model to "Tree of Life Upgrade" or another invisible one.
Abilities\Spells\NightElf\TreeofLifeUpgrade\TreeofLifeUpgradeTargetArt.mdl

Or try setting the model to ".mdl"