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Now this was a slick move. I assembled the wing without realizing I had a clear lens that needed to be installed first. Any suggestions how to fix this are welcome.
Not sure if this will work, but you might try this approach or a variation of it:
1) Take a long piece of thread and snake it thru the lens opening and out thru the opening where the wings join the fuselage
2) Use a very small amount of white glue to secure the end of the thread that is now sticking out of the fuelage joint hole to the outside portion of the lens (the part that is going to be visible from the underside of the wing).
3) Wait until the white glue is fairly well dried but not totally dry
4) Carefull pull the thread and the attached lens into the wing until the lens is near or in the lens hole
5) Use a small amount of clear part glue to secure the lens in the opening.
6) Let the glue dry so the lens is firmly in place.
The part I am not sure about is this: At some point you are going to need to detach the thread that was glued to the lens with the white glue. If you are confident that you have the lens firmly in place in step 5, you can possibly use a sharp knife to detach the thread from the lens at that point and then buff it to remove any scratches. The beauty of using the white glue to secure the guide thread is that white glue cleans up with water before it dries. So if you use the clear parts glue to secure the lens, you should be able to detach the thread from the lens by simply peeling it off and cleaning it up with water.
I've seen this approach used to pull side windows into place from inside a fuselage.
Hopefully one of our resident masters will be able to add the necessary refinements to this process.
Cut the square panel out with a razor knife. Install the lens and glue it back in place. You might have to put a spacer behind the panel to keep it level with the wing surface. You know a couple of flat stock strips to keep the panel from sinking behind the wing. Probably wont even need any putty/sanding if you take your time with the cut.