Use the light diffuser to corner the Orange Shoulder on one side of the and then catch him a few hours after lights out. :) Separating them would probably work too if you can leave the diffuser in the tank.

Sounds like a plan haha.

On a completely unrelated note, the yellowheaded jawfish that went in the DT at the same time last week, since appearing once on the second day, has not made an appearance since then. When should I start to get worried?

He's most likely made his home in some spot that is out of site. I have a pink spotted goby that I see maybe once every 2 months. I forget he's there. If your fish has died I would'nt go looking for it either, the worms in your tank have probbly already took care of diposing it for you.