It's not a perfect solution and I haven't checked how it works with Google Books or ARCHIVE but kind of does what I think you want for Project Gutenberg.
Create a custom column based off the ISBN option. Rename it whatever you prefer, I called it Identifiers, then in the template remove everything but {identifiers}. For Project Gutenberg books it shows you the uri, which in the case of The Adventure of Huckleberry Finn is
http://www.gutenberg.org/ebooks/76 You could then do a sort based on that column and it will group all of the Project Gutenberg books together.
As I said, not perfect but perhaps useful?