Now find a yarn darning needle or something similar and use the heat from a stove burner to carefully heat the needle hot enough to melt a hole slightly larger than 1/16th of an inch in diameter in the center of your plastic circle. Be sure to use pliers or an oven mitt to hold the needle so you don't get burned. The hole may need to be a bit larger depending on your couching fiber of choice and the size of your machine's needle. Try to keep it as small as you can to keep the yarn from escaping being couched down. If you make it too big, you can't make it smaller and will need to try again. Smooth any rough edges with an emery board or fine sandpaper.
I don't have photos of this next step, but you now center the plastic circle onto the foot and glue it in place with super glue. Be careful! The echo quilting foot has crossed lines on it indicating the center so I center the hole right there in the middle. Get it positioned just right before glueing. I didn't the first time and while I was able to pry the plastic off the foot, the superglue turned a bit opaque. If you get it right the first time, it is nearly completely clear!
Now put your fabulous foot on your machine and run the yarn or other fiber across your machine like this:
I made sure that there was plenty of lose yarn between the skein and my machine and kept all curious kids/animals away while stitching. My very first try, I was able to form this feather with the yarn. There were a few missed areas, but those can be stitched again and a feather is probably the most extreme manipulation of the couching fibers so it was a tough test!
Thanks so much to Leslie, http://marvelesartstudios.blogspot.com/ for inspiring this hack with her beautiful work!