For those not willing to spec into MM, do everything to maximize your haste. The Barrage has a five-second cast, so dropping your cast time of Tame Beast below that is obviously ideal, as the Barrage will not only hit you for a great deal of damage (meaning you'll easily die with the next hit), but it also interrupts your taming.
A simple method would be this: Haste Pot > [Deterrence] > Tame! It has a 98% chance of working successfully.
Try using [Scatter Shot] when he starts his Fieroclast Barrage, then [Deterrence] while taming. Scatter Shot reportedly will not have its disorient effect, but will still interrupt him.