macro one:
/focus <lockname>

macro two:
/focus <shammyname>

some other assorted macros to focus your other party members, etc

then just make individual healing buttons

/cast [target=focus] Lesser Healing Wave

/cast [target=focus] Healing wave

/target focus
/cast chain heal

etc etc

is the simplest way to do it



alternately, have all of the lock's spells be

/cast [target=focus] Incinerate

etc etc

and then just have him be the targetting bitch for your shaman, so your shaman's spells look like
/assist <lock>
/cast <heal>



Also have a look around for lock macros - there are some good click ones here. Micromanaging is for single boxers. Us boxers put it all in one key and smash it like a monkey on speed. You're working too hard!