Depending how your group does it, you can bane first set of dots with contagion on to slugs so they all convert at the same time, and you just LB2 all of them + boss, all other dps stays on the boss and don't bother with slugs, this is probably the easiest way to do it and have the highest DPS up time. If you're doing 1 super slug, i wouldnt even bother with slugs just stay on the boss since melee LB3 takes care of that. If you are doing burn.... well youre doing burn.

Do note that with higher gear my group doesnt have LB2 till the very very end, so better just do burn and melee LB the boss.