So my workflow is to go through the documents and use the snapshot tool to copy the highlighted bits. I put each bit into one column of a Word file, and the translation in the other column. It's nearly as good as comments in the PDF.
It seems to me that this would be a simple tool to implement: create the Word file, create the table, then every time I select something that's graphical, put it into the Word file for me and bring Word to the top. It's not a huge help, but it's the principle of the thing.