So far, I'm using... slaves assist party leader... leaderless party1 set-up where any toon can lead as well as any other.

Keybind: 1
#show Lightning Bolt
/cast [help] Lesser Healing Wave; [harm] Lightning Bolt

Keybind: 2
#show Chain Lighting
/cast [help] Healing Wave; [harm] Chain Lightning

Slaves add "/assist [target=party1]" between the two lines.
And with paging, current leader does not assist all slaves do.

I have a separate macro for Chain Heal, where each shaman targets the next shaman as their primary target, or themselves if that's not a valid target.
So theoretically, whichever shaman(s) are taking damage get hit with a heal which is not slowed down by taking hits.
And the secondary jump of healing power goes to the most injured team member thanks to blizzard's smart healing on Chain Healing.

In my mixed group, heals are all:

/assist [target=party1]
/cast [help] Regrowth; [help, target=targettarget] Regrowth; [target=party1] Regrowth

I have it set up for Lifebloom, Rejuvenation, Swiftmend, and Regrowth. The healer is a Dreamstate druid.