Okay, so first off the idea was to use LUA to script a spell, this is sort of a general concept right now but I'm sure people will be able to think of ways to elaborate it's usage.
Step 1: Make a spell
You would copy a spell that summons something, or replace some useless one, but have it summon the dummy unit.
Step 2:Make a dummy unit
Simple enough for those what I mean (Mainly from WC3), you make a unit that does absolutely nothing but is spawned when the spell is cast.
Step 3:Script the dummy
So now that you have a spell that summons a unit that does nothing, you use LUA! Script it so on spawn it will do what you want your spell to do and when it's done what it's meant for the LUA script will destroy the unit.
(For example, have your dummy target everyone within X yards and have a 50% chance to cast death touch on them)
Note: This is an idea so I want your thoughts, it's not a guide.