I would cut a sheet of freezer paper the length of one side border. Cut another sheet the length of the other border -- plus some extra for overlap -- and mark where the border stops. Iron the second sheet onto the first sheet where the overlap is. At this point you have several options. One would be to fold each border exactly in half, in half again, and again until you get sections that are approximately the size of your cable. I would use the template to draw the corner onto the freezer paper. You could also draw the template on each section to show you how to space (whether to squeeze or elongate), you could use the pattern to place registration marks on the quilt's edge (or use pins to mark), etc.