Pipe thin long lines (I used Wilton tip #4) onto parchment paper. Don't worry about the lines being perfect - you'll be breaking them up later. If you don't have a pastry tip, you can just cut a tiny hole in the corner of a sandwich bag.
Leave the sprinkles out to dry overnight.
Break the sprinkles up into sprinkle-sized pieces. You could use a knife for this, but it's just as easy to use your hands. They break up really easily.