Why not go 4/5/3/5, the first 5 will be rought but you should have purified healers at that point already so it wont be too bad, the last 5 should be easier cause youll have every healer purified by them. Tell the ppl inside to try to time theyre big add kills so they dont come out all at once, for instance a combat rogue going in can basicaly insta kill his big add, a lock or another dot class can keep dots up on the big sha while focusing more on the smaler ones first and delay the kill by alot so theyre big adds would never come out togetehr with the rogue one for instance. Also send whichever disc priests and mistweaver monks you have first cause they can also DPS the boss and they can finish theyre trial considerably fast since they can help the dumb NPCs kill the big add, Id go as far as saying send in all your discs and mws right off the bat, if you havent too many of them shouldnt be a problem at all, the healers outside can rotate CDs to keep everyone alive.