In my pattern, Kompeito, I use a technique to hold or reserve stitches for the armholes.
This is a simple technique that can be used in many ways; you can use it as we have for an armhole (you could also knit the sleeve down from that point), for afterthought heels on socks, the thumb on a mitten and even to position a pocket that will be worked when the sweater is finished.
In this method you use waste yarn to knit the stitches you want held. Then you slip them back to the left needle and ignore them until you want to work them!
In the video I show how to unpick the waste yarn and put the stitches from both the top and bottom onto double pointed needles.