Personally I just use

/cast [target=focustarget,help][target=target,help][self] Lesser Healing Wave

This will check if ur focus has a friendly target, if it does, it heals that, if not, it will check if the toon itself has a friendly target and will heal that if so. If thats not the case either the toon will heal itself.

For the fastest reactions you will probably want something more in the lines of:

/cast [target=toonname1] Lesser Healing Wave
/cast [target=toonname2] Lesser Healing Wave
/cast [target=toonname3] Lesser Healing Wave
/cast [target=toonname4] Lesser Healing Wave
/cast [target=toonname5] Lesser Healing Wave

on 5 different buttons. Cus there is always a short delay on you targetting someone and your alts 'knowing' you targetted something. (meaning if u target someone and u press heal too fast your alts will heal the wrong target, cus they dont 'know' you targetted anyone yet, which is caused by server 'lag')