Create a dummy unit, make it have none.mdl model. Set
Untitled Trigger 007
Events
Unit - A unit Starts the effect of an ability
Conditions
(Ability being cast) Equal to Frost Nova
Actions
Set u1 = (Triggering unit)
Set u2 = (Target unit of ability being cast)
Set l1 = (Position of u2)
Unit - Create 1 SpellDummy for Neutral Passive at l1 facing Default building facing degrees
Unit - Add Storm Bolt (custom) to u3
Unit - Set level of Storm Bolt for u3 to (Level of Frost Nova for u1)
Unit - Order u3 to Human Mountain King - Storm Bolt u2
Unit - Add a 3.00 second Generic expiration timer to u3
Art - Animation - Cast backswing to 0
Art - Animation - Cas point to 0
Create custom Strom Bolt, make it cost 0 mana, make it non-hero ability. Add neutral to targets allowed if it isn't there already.
I think that's more work than ordering a dummy unit to cast an ability.For the stun part, why not use a dummy with a Bash ability with 100% chance?
(I think it causes problems with ethereal units though)