Add {directory} as a Source DB field for the Rename function

Quite a few times now, I've wanted to use the directory that a group of files are in as the source field for a batch rename.  Can that be added as an option in the Source DB {field} rule?

For example, I may import a sound library that has a few subfolders in it named things like, "ambient", "FX", "voice", etc.  I often want to use those names for the category field.  Sometimes they get imported like that, but other times, the import process grabs an existing metadata field and uses that for the category instead.  I'd be a lot more efficient in cleaning that value up after the import if I can rename them all at once based on the name of the directory the files are in.