You won't get it to leave the original filename, however, you can get it to import the original filename as title. For that, in the adding books- preferences, change the regular expression (assuming that "02~001 The Colour of Magic" is your filename and should be your title) for reading metadata to
Then set Calibre to read metadata from filenames instead of content.
The downside of this is that you won't get any author or other metadata, unless that metadata is encoded in the path and you adjust the regular expression accordingly.