Well you folks really came through for me, thank you! A lot of ideas were presented, a few of which I'm going to give a try.
To recap, I'm trying to find a suitable solution for creating the "glass" for the rounded corner windows:
Australian traction modeler Bill Bolton comes through once again with the suggestion of trying Micro Kristal Klear. I've been using this stuff for gluing on clear styrene windows because it won't craze the plastic and it dries clear. But it also claims it can be used to make small windows itself. So since my bottle of Micro Kristal Klear is right here, why not give it a try?
Micro Kristal Klear is very similar to white glue, with some characteristics of rubber cement. I took a blob onto a toothpick and stretched it across the window opening. That was easier to do than I anticipated. Then I took a small screwdriver and scraped up the over slop. As you can see in the photo above, the "glass" is within the window frame. Not behind it as clear styrene would. Also, the "glass" the took on the almost 90 degree curve! But unfortunately that wouldn't last. Apparently it shrunk a bit as it dried and kind of straightened out:
And here is the result. Its not exactly "crystal clear" (which is probably why its named "Kristal Klear"), it is a bit cloudy, but not that much more than clear styrene. Also, since it is a liquid, the thickness is not consistent. So there is a bit of a "ripple glass" effect to the window. So Micro Kristal Klear is still a strong contender for use in the final model. But before I make a final decision, I'm going to try some of your other suggestions. Yes sir! Lets try some of those other suggestions!