Well, I don't know why I didn't think to mention this before, but I have (gasp) succesfully shortened an options cord myself using some scissors and glue. (I chronicled the experiment in an old thread, but I will summarize for you!)
Pretty much all you have to do is to pull the cord out of one of its little metal collars, snip it down, and glue it back in with some super glue (you may have to file the edge of the cable down to get it to fit). Hints: try doing it a little at a time, because you may find that 16" is too short for comfort. Start from about 20" and go down... I think I stopped around 18" because it seemed like shorter might not provide a wide enough angle when in knitting position -- also remember to account for the part of the cable that fits into the collar when you're measuring or you will end up cutting too much (not good).