With 5 shaman, you're going to want them all to be elemental. You're going to blow most stuff up short of heroics in one shot, so there's no reason really to have a dedicated healer. When I run my 5, I just bind all 5 to the same keys, so they all do the same thing. Then bind chain heal to a key, and all 5 can chain heal each other. The reason you see a lot of multiple shaman boxed groups is their synergy is probably the best you can get with 5 of the same thing.