i have had zero fortune with the fold'er feet with silnylon. i don't think it will work, the material has insufficient body for the effect to function.
what Does work is to practice with turning up the thread tension until things pucker, then backing off. using gutterman thread, the thinner of the two common varieties, and starting with a 5/8" seam allowance.
glue the good edges together with a bit of rubber cement and run your 5/8 seam. then iron it back on itself and run another seam 5/16" in from that. this gives a nice tight seam, and it looks ok.
do not be a'feared of bobbin tension adjustments. look it up on utube.
use contrasting color threads so you can see what the tension is doing.
hope that helps..