I stopped by TechShop on the way home from work on Monday to hop on a laser cutter and cut out a few pieces. All the lasers were technically reserved, but as I’d expected for a late Monday night, half the lasers were unoccupied. The pieces I cut were pretty simple long rectangular shapes, with 2 holes on one half (spaced 37mm apart), with a line of more closely spaced holes on the other half (see pic above), for screwing the piece into the servo horn. Since I didn’t know what the spacing was on the servo horn holes, I took a wild guess and cut a few different pieces with holes spaced 3, 4 and 5mm apart (I was using material fished out of the trash, so I didn’t care about wasting a few pieces).
Once I got home, I turned on my soldering iron to its lowest setting, and used it to heat up a part of the plastic to bend it into shape. The key seemed to be to apply the iron to the outside diameter of the bend, since that’s the area that requires the most deformation. Also, it turned out the servo horn holes were spaced 3mm, so one of my pieces worked out nicely. I might make a more compact version, but it works well for now: