Inspired by Guude's use of a turtle to save his dark iron blocks from being burned, I created a script to do the entire thing for me. It's pretty simple, but it gets the job done. I still need to add a couple safeguards (in case people feed it, say, dirt blocks instead of iron blocks for whatever reason), but otherwise all you do is input iron blocks in the bottom chest and get dark iron blocks in return at the top chest (I used enderchests, myself).
Link to script:
http://pastebin.com/bsgPufHH
The license (as if it really needs one) is
CC0.
How to use (also at the top of the script):
Screenshots: