There is an alternative method that is quite simple, every time you exit the shield/begin the fight, have a dps perform a single rotation on SC, it helps you escape that second DD, everytime I've used that strat we haven't gotten that second DD.
Even doing this just the first time out helps. The 1st 20% is going to be the hardest to get though. This is because by the time defensive systems kicks in and you locate where the shields are you should of burned off another few %. Done this for NM and it does help eliminate that issue.