I'd think Focus would be safer then Party1, as you can control your focus but not force the tank to be the party leader.

Still, you might want Focus to be free, for crowd control or such.

You could have your healer assist your active toon.
Assuming you play a DPS (or tank) and are targeting whatever is being killed.
You could then use creative assist macros for heals.

#show Rejuvenation
/assist [Your Active Toon]
/cast [help][help,@TargetTarget][help,@TargetTargetTarget] Rejuvenation

This will heal your target, if it is friendly; if not, it will:
Heal the target of your target, if that is friendly; and if that is also hostile, it will:
Heal the target of your target's target, assuming that is friendly.

If you wanted, you could add a last condition like: [@player] which defaults to healing your healer.