auger66, On the wall side, I would build a U shaped channel and fasten it to the wall. It would provide at least 2" of overlap on the shade, both front and back. The inside would be painted flat black, the outside to match the surroundings. My "U" shaped channel would have a 1x4 against the wall, with 1x4 pieces coming out in front and back of the shade. It would be built and painted in my shop, then screwed to the wall. If the shade would not clear a 1x4, I would use something thinner on the back and thicker on the sides. That's just something that needs to be puzzled out. I'm suggesting 1"x lumber as a starting point, but you can consider 1/2" thick and even 3/8" thick. I prefer to work with the more expensive pieces of either Aspen or Pine you find in the finished wood section of Lowes or Menards. I use screws for easy removal where I can, small nails where it is necessary.
The idea is that when the light strikes the back of the white shade and reflects back toward the window, it strikes the flat black surface and is absorbed. Some will still reflect onto the end piece, and is further absorbed by the flat black on that surface. What still reflects around will be absorbed by the inside of the front piece. The deeper the channel is, the more successful it will be. 2" is a minimum.
The center is obviously a greater challenge, but could most likely be solved in the same manner. Based on what I can see in the photo, I would do almost the same thing as the ends, but for both shades, so the column would be in the form of an "H'. I can't see in the photo how you might fasten it top and bottom, but where there is a will, there is a way.
The shade needs to come to rest on something so that light doesn't leak out the bottom. I can't see from the photos what the bottom of the window is like, but if there is nothing there, you might need to install a shelf along the bottom for the shade to come to a stop on. This would also give you something to set the "H" column on. You would probably need a bit of a lip on the front of the shelf to block light.
When all of this is painted the color of the surroundings, except for the inside of the channels, it just becomes part of the decor and is quite spousal acceptable. Mine are stained, but you can see that it just blends in with the wood work.
Remember, the 2" is suggest is only a bare minimum. A greater amount will do that much more good.
Plugging light is like stopping water leaks. You have to stay at it until you get it right.
If this proves confusing, just ask any questions you may have.