You could bind the mouse buttons to warcraft buttons.
So you can either click the button in wow.
Or press the mouse button, which clicks the wow button.

Then include the logic of [mod:alt] and [nomod:alt] as needed.

If your software supports mouse broadcasting (HKN, ISBoxer), consider Repeater Region based heals.
Set up Grid, Healbot, OpenRDX or Vuhdo to display the team alphabetically.
Then go with something like:
Left Click = Lesser Healing Wave
Alt Left = Healing Wave
Ctrl Left = NS Healing Wave
Right Click = Riptide
Alt Right = Chain Heal
Ctrl Right = Earth Shield