I'm eyeing this tool, looks pretty slick
http://www.klann-online.de/englisch/Filme_E/KL-0369-31K_E.htm
but i'm not sure if it will work with this engine.

An independent Mercedes mechanic snapped off the one in my vehicle, but I removed the remaining plugs. I found a combination of Kroil and biodiesel did a great job of breaking up the carbon so that I could remove them.

After the plugs were out, biodiesel on a Qtip cleaned all the carbon out of the head. Did such a good job, I was able to thread the new plugs in by hand (hand only, not even a socket) all the way in till it seated.

I guess Hatterasguy has a good idea, but that huge intake manifold is a pain to remove each time.