Couching is simply sewing a heavy thread in place with a finer thread. It works beautifully by machine as well. I use a zigzag stitch to secure the heavy thread in place. And, if you have a cording foot— the foot guides the thread as you sew.
a way to use large spool of thread on a standard machine. set the spool in a heavy cup and bring the thread around the spool pin so it makes a 90 degree turn to the thread guide. Set the cup directly under the spool pin.