I had an anthias that only ate mysis as well. When I had to go out of town for a couple of days, I put an auto-feeder on the tank with small pellets, and hoped for the best...
When I returned home a few days later expecting to remove a dead fish and a large water change due to the ammonia spike, I was surprised to find the anthias took to eating the pellets with extreme vigor, and actually refused mysis from then on.
Edit: This was in my QT, not DT...
When are you leaving to go out of town? Perhaps you have time to ween this fish over to small pellets before you go...