Step 3: Sleeve Cords
The longer piece can be more quickly done by hitching the cord to the inner strand(s) you saved, and pulling most of it through.
Unfortunately I haven't bothered to research the best way to do this without the temporary joint of old gut and new gut at some point breaking apart. I just use tape, and when it comes out alone I push the remaining cord through using peristaltic action: push the tip forward a tiny bit to form a compression of sleeve while squeezing behind the tip, then squeeze the sleeve around tip, and pull the compressed sleeve backward, undoing the compression (repeat). It takes a while if you didn't get most of it already pulled through.
Once you've sleeved them, use some heatshrink tube on the ends of the ear units and plug to tidy things up.
Note you may need to hold the paracord ends underneath in place using electrical tape if the design flares out and will not accommodate heatshrink without it slipping off.
Addendum 2010 06 22
Anyone want to experiment with also feeding a semi-rigid monofilament/fishing line through? I imagine that knot resistance could increase by doing so.