It's very difficult, particularly in confined spacees like this. First of all, don't get overexcited about it, since its unlikely the player will see it. Waypoints aren't actually much good here, because they pause at each one and anyway waypoints are quite big.
It's probably worth playing with invisible markers/gamelogics and the commands doMove and doFollow.
Set the markers along the path you want the loons to follow. Create a script, called when you want the execution parade to start. Get the guard to follow the markers and the POW to follow the guard. You will have to experiment to make it work, and I'm not saying that it will work at all, just that it's probably worth a try.