You can set up your heals as one of two approaches then.

a) Target of Target.

#show Renew
/assist <target=focus> (or whatever)
/cast [help][@target,target,help][@targettargettarget,help] Renew

This will assist your leader.
And heal their target if it's friendly, or the target's target (if that is friendly, and the target is hostile), and the last conditional is for PvP really... targeting a hostile who is targeting a hostile who is on a friendly (example a horde healer (you're on) who is targeting/healing a horde DPS, who is on one of your friends).



b) Target specific heals.

Press this hotkey, and your healer does this.

Ctrl 1 =
/cast [@Cuddles] Renew

Ctrl 2 =
/cast [@Huggles] Renew


Do this for as many heals as desired.