You're gonna have to starve him, but ime aros are greedy so it shouldn't be to long, but my experience is just with a silver so maybe it was just him, he took to pellets after about a week of not eating at like 6 inches.
My new XB is now eating pellets after 1 week of stuffing MP with Hikari pellets. My wife phoned me this morning and told me he has been eating 6-8 pellets the past 2 days. WooHoo.
There is more than 1 way to train, and each fish is different.
Larger fish can be starved for a very long time. The case with my old XB.
Smaller fish can be starved for short periods or tricked by feeding with their favorite foods.