I think you might find more success as:

Prot Pally
3x Ret Pally
Elemental Shaman

That way, you still have 4 DPS for faster clearing, and can rely on the 3xRets to provide most of the healing needed for most encounters. The chain heal of an Elemental Shaman is still pretty decent if you have to top off people for most AoE encounters. Run WF, Healing Stream, Str/Agi, ToW (or Magma) and just have the Shaman pew pew for most encounters.

Dual Spec him, but I bet you wouldn't need to pull him into full Resto that much...