I have a heal anyone option on my healers, but I just don't advertise it a lot, since I don't use it a lot and it gets people to think they have to target someone to be able to heal. Again, I almost never target anyone to heal, I just heal whoever the mob is beating on.
/cast [target=focus-target, help] HealSpell
should heal whoever the main has targeted. It works for BG's, people outside your party, or emergency heals in your party. I put that one first and the heal focus-target-target second.