@certainly The plugin was only ever a quick thing I just made for this thread here as a proof-of-concept, and it only lived on that Github gist. Looks like it got accidentally deleted. I don’t have a copy, and actually I didn’t even remember it.
It sounds like a nice idea, though. If I find the time I can take a look at this again and try to create a plugin for Picard 3 (and this time store it somewhere proper). Right now I don’t even remember how I implemented the functionality, I really wonder how I did this.
If someone following this thread has a copy somewhere, please share 
Update: nevermind, I found a local copy. It’s a nice plugin really Give me some time to port it to Picard 3.