You could insert a oblong piece of flexible clear plastic to the back of the collar. Cut a 1cm slit in the back of the collar (on one side of the material only) and slide the plastic in with enough protruding so it doesn't get 'lost' in the collar itself. You could put a pinprick hole and sew the plastic to the edge for securing. Fine blanket stitch the 1cm slit to prevent fraying.
Be careful when ironing and use a dampened handkerchief to prevent melting and scorching.
Paula M
May 2009