Ok, work with me on this one. If I recall your room layout correctly, it's the left surround mounting that's the real problem, since there's a big window along the entire wall. You have a useful wall to the right of your couch, so that's not a problem. Am I correct so far? Good.

My idea for your left mounting involves placing a spring-tensioned or otherwise securely mounted vertical pole in the window area at a point where the cutains come together. Then attach a piece of scrap wood to the pole with a couple of U bolts. Then either mount the included T-bracket directly to the scrap wood or, for a more aesthetically pleasing look, mount an FMB or other bracket to the scrap wood which would allow you to poke the speaker through the gap between the closed curtains.

What do you think?