I finally solved the “rounded corners” problem with the custom matching subtitle font. Click the image below for a higher-res version:

Top is the custom font, bottom is from 35mm elements (DeEd 2.5). FWIW, the blur on the font matches a little better in practice–I scaled the top image down from 1080p to 720p in Photoshop, and I think it applied a sharpening filter.

Since, at least for my purposes, people will not be seeing subtitles containing the exact same text placed right next to each other, nor will they really even be seeing the alien subtitle text in this font at all, I think this is more than good enough. You really don’t see the transition between the theatrical subtitles and the font-generated ones at all anymore, even if you’re trying pretty hard, so fans of the matching fonts will be in for a nice surprise in 9.1, which is still a while away yet, due to other major changes.