I would still use Focus

#showtooltip Healing Wave
/cast [target=focustargettarget,help,nodead,exists] Healing Wave; [target=focustarget,help,nodead,exists] Healing Wave; [target=focus,help,nodead,exists] Healing Wave

or you could use

/target toon1
/cast Healing Wave
/cleartarget

/target toon2
/cast Healing Wave
/cleartarget

/target toon3
/cast Healing Wave
/cleartarget

And hot key them to F1-F3, or whatever you like.
With these 2 macros you have the option to have heal focus, or focus target, and heal each toon in situations where Focus isn't fast enough.