Sharing this hack in hopes it helps anyone else.
TLDR; if you have a print job running and realize it’s doomed to fail because it should have support, tape down some index cards and carry on.
I wrote this up in an even longer blog post, but the quick version is that I saved a print that should have had support by taping index cards to the print bed and making them match the last layer before the overhangs started. Saved the print and the surface quality is actually pretty good considering it was doomed otherwise. Makes me wonder about the possibility of making some shims just for this purpose. Could even make custom support for a particular part and drop it on the bed just in time rather than layering out the support scaffold every time you run the print (probably only useful for large quantities of a given print).