quoting myself for this

What I usually do on vexallus (4 shammy 1 priest setup)

4 x lighning shield, 2 earth elementals and 2 fire elementals, then just pop heroism, trinekts, and nuke like mad

lb-lb-lb-cl rince repeat. Somehow the combination of lightning shields and the elementals take care of the adds (this is what I use on heroic, i cant remember what I did on normal but I'm prety sure it's the same thing, just a lower gearrequirement)
I run 1 healer instead of a 5th dps, but I'm prety sure it would work just fine with an extra dps instead, as the fight will end faster!