when I worked for a living we would use a grade of wire to form staples to hold books together and if we put too much pressure on the pusher bearings it would make the wire flat like a desk stapler uses. I would think you could adapt that theory and with a sleeve over a bearing with a groove cut in it to the depth and width of what you want the round to be, then put pressure with the second bearing pressing the wire to make a flat or a D shaped wire. All you would need to do is pull the wire between the two surfaces. My 2 cents out of the box