This is just theory, as I havn't tried your exact group.
But, I would think it would be easier to use the Shaman as your main, then have your hunter and Warlock DPS with pets (tanking) + spells.

Depending on your cast times for the Shaman and Warlock spells, you could bind them to the same key, or even spam a single macro (different for each class).
It would probably make for easier off-healing when needed too.

I know this isn't exactly what you were looking for, but I'm interested in anyone elses input on this too. :P