First attempt:
100shm/tank merc, 100pal/healer merc, 92 pal/healer merc
engaged normally melee and the 2 healer mercs died fast followed by everyone else in short order.
Switched up a little:
100 shm/tank merc, 100 pal/healer merc, 92 pal/wiz dps merc
Let the tank roll in and kept everyone else back to heal / dot. Tank merc died around 5% and the shm tanked the rest. Not pretty, but it worked. No raid gear whatsoever.