I might check your gauge and see how many inches wide you need it, and do some creative math work. I am trying to do something simular to a pleated skirt pattern.
I am trying to expand a 29 inch waist to a 38/40 inch waist. So what I will do is find my gauge, see how many stiches are in the pattern, and adjust the to the nearest stitch count.
I am sorry I can't be more help....