Rather than making the windows taller, you can remove the top, take it to an auto top/upholstery place and have them run a stitch line parallel to the existing one above the window, but one inch closer to the window. Works like magic.
If you know someone who is a Quilter with HD or leather/vinyl needles, they could do it, too.
And @Bob: IM S6 you sound like a candidate for an Espar gas heater! Nice and toasty inside - Leave your coat at home!