Furious Slash is a last priority ability for Fury, all the guides adice to "use it when you cannot use anything else". For instance, my last Odyn's attempt I used it 25 times in 10 min fight, which is almost once in 30 sec, hardly ever.
If you replace the use of FS with WW you will get a passive cleave but very minimal. What I meant initially your guild mates should not try to actively cleave the add (by using WW every time before BT or Rampage), just alter the rotation slightly as I mentioned. It will maximize their output on the fight.