Using an FTL setup, I use my G keys for heals from my 4 Rets.

G1 = all heal toon1 (the prot pally)
G2 = all heal toon2 (ret pally1) ..etc thru to G5.
G6 = all heal self (except the prot pally of course) - useful if I'm taking AoE damage.

Works well for me anyway, and in fact I might drop the healing back a bit, as 4 heals from the rets is a major overheal, so I might use a /castsequence in front of the heal macros to have only every 2nd ret pally cast the heals on G1->G5.