You know, I actually did something that (attempts) to fill a similar niche in the GitP PrC contest -
the Voidblade Eliminator. You might be able to plunder it for some ideas, though I'm not certain how successful they are at attacking casters either (though now that I'm thinking of it, they
could use Armor of Absence to be 'not there' for various
contingenciesand the like....).