Death Grip would help with runners/casters, as would Hammer of Justice slightly, Exorcism, earthbind totem and root. You can also strangulate/mind freeze casters (DK skillz). I've thought of this too. You could position your group, DK would pull the mob to you and your melee would chew em' up. Once you got it down you could get slick enough that you pull with the mob's back to the rogue/druid. 2 ret pallies, I assume? Holy Pallies are as useless as tits on a boar hog, for 5 man healing, in my experience. Especially considering your group has a chain heal, nice HOTs if needed and Tranquility if things really go south.

Another plus to this setup is that now gear drops would be wasted (plate,mail,leather and cloth). I run 1 pally 4 casters and all I get is mail and leather :/