You can watch their Berserk icon timer and as soon as it wears off is when you can dispel the pacify (GCD will hit after the 1). We have our Warrior do the pull Defiance-Unchained in A1S for the most damage before the split, and I usually can catch the 2nd pacify before I have to go back to refreshing HoTs. (First pacify is null by the Bard's Warden's Paeon). I don't always get it if his Berzerk timing is off than the usual but I'm pretty concious if it's possible during raids.