[Espeefan]

I would just cut the window out. Should be easy. Mark where you need it to be, grab a small drill bit (like a #80 or so), and drill around the edge of the window frame. Make the holes close enough together so it takes minimal cutting with a hobby knife to finish it up. Cut from hole to hole, then just file or trim along the marked out window frame edge. Easy. Even for me, and I'm horrible with bodywork!