[porphyry5]

Is it possible to have calibre add such metadata-less ebooks to its database and then manually create metadata for each such file?

The full story: I originally created these txt files with calibre from epub originals. I no longer have either the epubs or the opf files that calibre created. The ereader I used then, an iRiver StoryHD, used the standard directory tree structure to organize its files and made no use of the metadata at all. Unfortunately it died and I now have a Sony PRS300 which creates an elaborate database for file access from their metadata. For files that have no such metadata, the result is an indigestible mess.