Chop some old three strand line into lengths about the diameter of the finished barrywrinkle. Streatch a longish bit of marline between whatever's handy, and start hanging your little bits, doubled at the middle and secured with a cinch knot. Really just amounts to draping the doubled yarn over the streatched marlin and pulling the ends through the bight. I leave a bit of marlin free at each end to make a siezing to start and finish it. Essentially, just wind it around the stay.
Rope breaks down from strands to yarns to fibers.
Ashley's has a nice picture of the fabrication setup, too. Spectra and the like are even better, as it doesn't absorb water. So the next time your racing neighbors junk a halyard, consider recycling it. Makes eternal doormats, too. Finally, strips of carpetting make really quick, very effective baggywrinkle.