So part of the problem seems to be that you don’t use a album based folder structure in this case. The question is why do you want to have an external playlist anyway, it’s read-only for Roon. You might be better-off using Roon’s own playlists or smart playlists (bookmarks).
- Playlists
- Create Playlist
- FAQ:How can I find tracks by path?
- FAQ: How do I create a smart playlist? How do I save a Focus?
- FAQ: How do I select songs or albums? What can I do?
Find tracks by path seems to be what you’re looking for, storing the filtered view as bookmark or (multi) select the tracks to create a playlist.