Yep - it's as easy as pie to put a link to a file or folder into an "Arbitrary Identifier"
In Look and Feel->Book Details->Arbitrary Identifiers (it's a wide button labelled "Create Rules to convert identifiers into links") enter fields such as this
Key:bookfolder | Name:Book Folder | Template:file:\\\{id}
Key and the Name can be what ever suits you, the Template shown is what worked for me on Windows, it may may need to be otherwise on OSX and/or Linux. Arbitrary Identifier rules are global, i.e. they apply to all libraries.
The first step is to get the path to the Anthology into the clipboard. Use the
Click to Open link in the Book Details panel of the Anthology to open a file manager window, copy the path to that folder to the clipboard, close the file manager window.
Next for each split-off book open single Metadata Edit window. If the Identifiers field is empty you can simply type the Key, a colon, and then paste the clipboard and you will have something like this
bookfolder:D:\Calibre Libraries\_Test\Charles Dickens\Anthology 1 (367)
If the IDs field isn't empty right click in it and select "Edit Identifiers in a separate Window", the existing IDs will be listed, just tack the bookfolder:blah blah on the end. In the Book Details panel you will have a clickable link named with whatever you put in Name - eg Book Folder
Idea for a 'Book Linking' plugin, it would have a copy book folder path to clipboard item, and an Edit Identifiers item which would leverage the one in Metadata edit, it could have something to display, and maybe select from, the list of Arbitrary Identifier rules. Maybe it could have an option make the metadata.opf readable.
BR