I took it upon myself to attempt to write a guide to multiboxing death knights, but I have yet to finish it. I'm basically halfway with it (I played the area through once just to see it and understand it). I don't know if I'll keep going - they just don't interest me in a group - It would be more fun to box them with shadow priests or something like that. There are a few addons that put a HUGE runeblade with rune cooldown information just below the center of the screen and that's how I've been handling the different spec issue. It seems to work well enough.