Damage type of abilities

Ok this is either incredibly easy or incredibly difficult - is there a way to have Abilities do damage with damage types other than "Spells."

For instance, say I want a firebolt spell to do Chaos damage, or a starfall projectile to do Piercing... Is there an easy way to do this, or will triggers have to come into the equation?

All help is, as always, much appreciated.

// Ligature

Only thing I can think of is using dummy units.

Like, when you order a unit to cast Firebolt, have it deal 0 damage (stun as normal) and have a trigger pick it up and create a dummy unit to attack with no attack sound for however much chaos damage.

Or, for Starfall, create a dummy unit with the desired attack damage, give it the Starfall unit projectile, summon it when Starfall is cast and have it automatically Hold Position (a range attack will automatically pick up enemy units)... then destroy it when Starfall's channeling is stopped or cancelled.

I was afraid you were going to say that...