Please comment and vote.
Step 1: Tools and materials
~2m of 4 core speaker cable, $3-$4 (this was complete overkill. get thinner cable)
2 speakers, $4-$5
stereo jack, $1.95
headphone thingy, free from airline.
The tools list:
hot glue gun
dremel (not shown)
Step 2: Cut the coconut
drill hole through eye of coconut
put coconut in vice
with a cross-cut saw, cut not through the eyes, but the other way
get a butter knife and start prying the flesh out
eat flesh, drink juice, or make coconut milk
Step 3: Drill hole on the top of the coconut half
Step 5: Making the headphone thingy comfortable
As my headphone thingy was very, VERY uncomfortable (to the point of pain) with the coconuts on them, I had to make them wider. Yours may not be uncomfortable, so you are lucky and won't have to do this step. But for everyone else, here's how you do it:
Stretch your headphone thingy over something, ie a vice, under your desk etc. and start attacking it with the heat gun on max. When it is pliable enough, hold it in the position you want, and let it cool. You have to keep tension on it the whole time, other wise it will return to its former shape.