You can use /cast [target=focustarget] spell. Have your slaves make the main as their focus. You can also add additional modifiers in the same macro



/cast [target=focustarget,harm] lightning bolt;[target=focustarget,help] lesser healing wave


Edit: Sorry should clarify a little further. If your main is targeting a mob it casts fireball. If he targets a friendly it casts heal.. you can play around with it too.