We just have a small kill group with a healer go to one side, while the rest of the raid goes with the boss. Kill add while passively cleaving to boss. The other group finishes, meets up with us and we proceed to let the boss channel for as long as we can manage.
60% of your raid isn't going to lose DPS moving to the add that's going to be cleaved with the boss lol, and you're going to be gaining damage from the cleave that you would be doing when you kill the adds to begin with. The kill group has a bit more travel time, but you just put mobile people in that group and use warlock gateways to get back to the group fast.