Step 1: The ingredients
2. iPod shuffle, or other light-weight music player. The shuffle claims to weigh 0.78 ounce (I didn't weigh mine). Substitute a heavier player at your own risk-- of headache.
3. An inch or so of Velcro (not shown, yet).
4. Implicitly, you will also need a soldering iron, shrink wrap, wire cutters, and so forth. If you aren't comfortable with these, maybe it's time to go shopping for a nice new set of wireless headphones!
Step 2: Shorten the cable
Cut the cable in two places, about three inches from each end. (Save the center section for a later project.) Strip the two exposed ends. There are three wires that go through the cable (left signal, right signal, and ground). The wires are color coded, so you can just solder the three pairs of matching colors. Use heat-shrink tubing or electrical tape to keep the three solder joints from touching.
As you can see in the photo, I used a piece of black heat-shrink tubing over the three pairs, which makes the splice nearly invisible.