...yes, it is finally cracked!
Phew! After many months filled with frustratingly unsuccessful attempts, I finally understand how to access HG/SS saves. And guess what? It is ridiculously easy to do (once you know how to do it), but figuring it out took *much* longer than expected.
Attached to this post is the latest version of my tool, which includes a Readme file that tells how to set up (almost) everything. If you want to have a look at the source code, I am releasing it under the GP