I'm not sure why this works for me, I found out on accident. When i hex stuff, I just target them with my paly, and the girls target his target. when i pull the hex and start dpsing and their target never changes, but they dps the mob I'm on. I use /castsequence [target=focustargettarget] macros. It works well. I normaly hex two mobs tops no matter how big the pull. I target the same mob with two girls and the other with the last two girls. IF hex breaks too early I just rehex, they still have that mob targeted. Wierd.

Now that my paly has 24k HPs unbuffed, I often will not re-hex. I have pulled 5 heroic mobs many times and hex broke right away, so i was tanking all 5 and had no deaths.