I found some 2 1/2" blinds that I really liked and spoke with the company's service department to see about getting custom trim to cover the gap left by regular blind trim. They told me that it could run a couple hundred dollars per window, and that I would need to trace the shape with a piece of paper and send it in to them to cut.
The trim that came with the blinds is just the standard window casing that I used to trim out my windows. Each piece a notch cut out of the back, so that two metal pieces could be placed in the notch and then twisted to lock them in place. It was kind of an upside T shape to the groove.
I decided that if the window company could cut a shape from my paper tracing, then I could, too. I initially thought to just replace the whole trim for the eyebrow, but I don't have a router bit to make the T shaped groove. I didn't want to wait to get one shipped to me, and I didn't want to worry about getting it straight.
I decided to join a new piece of casing to the shipped trim. I traced the curve with the standard trim installed and marked the top of that trim.
Using my DeWalt multi-tool, I cut the curve and then sanded the edge. The bottom line of the trim in the picture looks a bit wavy, bit it is the factory edge, so it is straight.
I then glued the new curve to the standard trim. It took a lot of clamps, and I used some nails for additional strength. I also put tape along both edges so when I finally caulked the gap, clean up would be easier. Any extra caulk would pull off with tape.
I did need to spot sand a few areas to make sure they had a good fit. A coat of paint on each window blind trim in our standard trim color brought it all together.
I am really pleased with my $4.53 solution!