This is what I've been using:
[build=OQQUc44R1KRWCpFqMja5i9F5F7gA]
Tact 4+1, Str 7+1+1, Sword 10+3, Curses 12
94% of the time you should kill them all (per raptor, so slightly less?), 6% of the time you kill all but boss ([1-.75]^2). I'm thinking you might be able to bypass using a 2nd MoP or EBSoH, and simply use [finish him] on the boss afterwards? Might try that, should be 100% (with 1 extra slot, hmm...).
EDIT: This one seems to work, and you can still 2x MoP:
[build=OQQUc4oQ3qRWCqM6F9F5F7g2k3gA]
Tact 6+1+1 (or 6+1+2

, Sword 11+3, Curses 12
Paragon runner as usual with shout buffs. At entrance to cave, mark a raptor with 1, then tab to next raptor. Ball them all up, then 2,3 and 1 on next raptor. 4,5 as they get closer (3 wears out), then 6. If boss still alive, 7 him, move away, then 8 over and over. I tested with a single MoP and pulling only 32 of 33 raptors, and it took 4 necrosis (2 YMLaD) for the boss to drop...