How to make ability invisible?

Hi

ok my problem is: there is a unit refers to an event and i want this unit to order to cast an ability, but the unit doesn't got this ability. Is there a way to do this or give that ability to this unit but make it not castable by the player?

thx for help

€: the ability i want to order the unit is whirlwind(bladestorm)

I'm thinking that if you add the spell to a spellbook, give the spellbook ability to the unit, and disable the spellbook it may work. I've never tried it, but it works with passive spells so it might work with active spells.

I will try it, but pls tell me how to add the item-ability to an unit? wich trigger do i need ?

€: will search in forum