Demo "scripted" battle with Non-party character?

I am trying to do a cutscene where a character (not in the party) is attacked, Battle starts, and the character uses a magic attack and wipes out the enemies. None of the PCs should be involved in the battle, but otherwise it should look just like a normal fight but with the NPC choosing (scripted) attack options, etc. 

To be more specific, the party is talking to the leader of the army unit fighting the monsters, a monster jumps the leader from behind, a battle starts with just the leader and monster, the leader chooses "Magic" then "Fire 3" the battle progresses, the blast goes off, monster dies, and the victory animation plays, then the battle ends and we're back to a series of show-texts like a normal event.

So far the only option I've found would be to make a party of just the NPC, fight the battle as I want it, record it using a screen-capture program, and then play it in-game as a movie... From some of the things I've read on here, it's possible without using scripting, but I cant figure out how to do it... (especially with non-party-members)

Suggestions?

EDIT:

The NPC _is_ setup as an actor with all the stats, weapons, etc.

Did you try using the Force Action command?

You can set up battle events for a specific troop in the troop tab of the database. There you can set up force action events for both actor and enemy. Just set the party to just this one actor and make sure he has the automatic combat trait on him.