How can I make and sew a drawstring hole half way along Sewing Machines Parts and Sales in Los Angeles

So, I was hoping you guys might be able to give me advice on how to approach a project (my first foray into sewing) that I’m working on. Essentially it’s a down quilt for camping, but it needs a drawstring on the top and bottom. This imgur album with a picture of the kind of drawstring and the construction of the seams.

Basically, the top and bottom pieces of fabric have 3/8″ hems, and then are sewn through together along the hem line, before being rolled twice to form a 1/2″ hem and then sewn across (the photos do a better job of explaining). The cord can go inside the 1/2″ hem, but there needs to be some access to in the center. If I just cut a portion out of the middle then there are going to be un-hemmed edges (or at least a point) which won’t be great with the nylon.