The Fontself beta that automatically generates the missing case was just sent to you. This means no need to mess with glyph duplication or copy/pasting kerning values.
If your font includes absolutely no character from the other case (upper or lower), upon Save and Install, all the glyphs in your font will be mapped to the same characters of the opposite case.
This will also map alternates, ligatures, kerning pairs & kerning groups. So you really have NOTHING ELSE to do to support single-case fonts. How cool is that? 
Please keep us posted on how the features fares on your end. Enjoy!
@johnmisael @brick @DavLedo @harleycreative @Koazar @Hybi