The old Stretch and Sew also taught that when you sew knits GENTLY stretch the knit as it moves under the needle by holding the fabric in front of and behind the needle. this puts extra thread into the fabric that allows for a little stretch. This would work for a very small zig zag as well. In case the fabric looks stretched out when you use this technique, all you have to do is wash it and the fabric and thread will relax into the original shape. I've used this technique a lot and it works great.