U should use the channel ability in combination with triggers.
The channel ability will be a dummy ability that starts a trigger, this trigger usualy creates a dummy unit that casts the actual spell.
The spell the dummy unit will cast has the projectile art aswell.
Ofcourse the trigger also creates the special effects sometimes.
I hope this will help you since the channel ability itself does not have a projectile art like Steel_Stallion above me stated.