Special thanks to Maqs and thinus for helping me solve the problems with this.

Place this set of macros on each Shaman (assumes 5 shaman). For each one, rotate the cast of Healing wave by moving the commas around. What I did was put ",,,,Healing Wave" on the shaman who's macros list I was in (So that the shaman heals THEMSELVES last). Then I went all the others, starting with "Healing wave,,,," and wrapped around. This way I didn't get duplicates.

For Example:
/castsequence [target=Gorehack] [help] [modifier:ctrl] reset=5 Healing Wave,,,,
/castsequence [target=Gorehand] [help] [modifier:ctrl] reset=5 ,Healing Wave,,,
/castsequence [target=Gorehell] [help] [modifier:ctrl] reset=5 ,,Healing Wave,,
/castsequence [target=Gorehound] [help] [modifier:ctrl] reset=5 ,,,Healing Wave,
/castsequence [target=Gorepig] [help] [modifier:ctrl] reset=5 ,,,,Healing Wave <--- This is Gorepig's macro list

You can see how I looped the sequence around.

I mapped each macro on F1-F5 and just put them in the order that the shaman were on my Main's screen. What it does is if I hit <ctrl-F1> someone will always heal Gorepig. If I don't hold down a modifier, F1-F5 act exactly the same as they do with default bindings.

I can also stagger/chain these if one is taking a lot or consistent damage.

Works great!

Full macros below. Let me know what you think!

MACRO 1 "Gorehack" Spell_Nature_MagicImmunity
/castsequence [target=Gorehack] [help] [modifier:ctrl] reset=5 Healing Wave,,,,
/stopmacro [modifier:ctrl]
/target Gorehack
END
MACRO 2 "Gorehand" Spell_Nature_MagicImmunity
/castsequence [target=Gorehand] [help] [modifier:ctrl] reset=5 ,Healing Wave,,,
/stopmacro [modifier:ctrl]
/target Gorehand
END
MACRO 3 "Gorehell" Spell_Nature_MagicImmunity
/castsequence [target=Gorehell] [help] [modifier:ctrl] reset=5 ,,Healing Wave,,
/stopmacro [modifier:ctrl]
/target Gorehell
END
MACRO 4 "Gorehound" Spell_Nature_MagicImmunity
/castsequence [target=Gorehound] [help] [modifier:ctrl] reset=5 ,,,Healing Wave,
/stopmacro [modifier:ctrl]
/target Gorehound
END
MACRO 5 "GorePig" Spell_Nature_MagicImmunity
/castsequence [target=Gorepig] [help] [modifier:ctrl] reset=5 ,,,,Healing Wave
/stopmacro [modifier:ctrl]
/target Gorepig
END

NOTE: Thinus mentioned that the last 2 lines could be summed up as:
/target [nomodifier:ctrl] NAMEHERE -- but I haven't tested this yet

Edit: For clarity