Thanks for reminding me of that option to go through the speaker.
I tried the coat-hanger routine and was VERY gentle--for fear of cracking the face plate (as I understand it's about a $550 mistake). I put soap bubbles all the way around the instrument cluster and applied alternating tension with the coat hangers.
However, I didn't get the instrument cluster out--and had finally resolved to buy the proper Mercedes tools.
But I like your idea. I will give it a try.