With felt hats and the like, a lot of us use hair spray to stiffen it. You could also run some light wire on the inside of the seam. If you turn the pants inside-out, see if the wire would go under where the extra material is fold back, then glue it down with a light touch of fabric glue. Test any spray of glue to make sure it doesn't stain the fabric (like on the part that would be hidden under the boot)
Hope that helps.
Hope that helps.
