Might as well share, I'm sure some people have figured it out by now anyways.
You can stun Inferno Drop with ANY WS. You won't get a "stun" message, instead it will say Inferno Drop fails. What we do is make sure we always have TP ready for stunning, I personally use Follow Through, but anything will work. The more WS's that you get off, the higher the chance to stun it. So don't assign an order, and don't assign just one person for stunning, it's a group effort.
We're unsure if it's the action of using a WS itself that stuns it, or if it's the amount of damage he sustains while readying Inferno Drop. We do however know that it has proven to be a good strategy over and over again. We might miss a stun here or there, but least we're not getting spammed. Rarely does anyone die if he gets one off.
As far as the hate issues Xquiel is concerned about, Istinto pretty much summed it up. Let your tank(s) secure hate when your first start the fight. Nobody should be attacking at all for about ~30 seconds after first engaging.
Overall the most important things about the fight are positioning, hate management, reaction speed, in that order.
Good luck