I don't have a drill-column at my disposal so designed this Dremel attachment to center the 8mm bolt while hobbing.
Pictures say more than words....
Print out the pdf from http://www.thingiverse.com/thing:9291
Modify the scad file to let the holder fit your Dremel snugly.
You might wanna make the 8mm bolt slot a bit wider to move the Dremel without friction (I heated my holder to bend it a little)
Put your 8mm bolt in a vise.
Put the printed pdf on top (first make a hole in the middle) and fix this paper.
Dremel your 8mm bolt in 16 steps using the indicator.