Try heroics with 4 ele shammies, you can do a bunch of them that way without a problem. Eventually however you start wiping a lot on the harder heroics, and you will find having a resto shaman can help out a lot. It really is doable either way imo, it does require adapting quite a bit to put a resto shammy in the group. Some people use /stopcasting macros and have seperate buttons for heals, I don't use that since I found GCDs were causing my heals not to go off (dunno how the ones that DPS & heal deal with that). It does take some time to adapt if you respec one to healing, but I think most of us clearing the harder heroics (Anub/Old Kingdom, Stratholme, Halls of Lightning, Utgarde Pinnacle, etc) found it very helpful.

If you haven't leveled any to 80 yet, you may want to think about multicomp too. imo a priest makes a superb healer when geared up, better than resto shaman for multiboxers. Also a mage or boomkin is nice in the group as well.