A nice offer thanks. Don't suppose you run from source by any chance? As Kovid has been nice enough to make a few tweaks to things as this is coming along but you will likely need to be running from source to give it a go until the next Calibre release.
Any volunteers, PM me an email to send you a zip in the next day or so. Functionally the metadata downloading is all working now, I've just started work on the custom genre->tags mapping configuration. So it should be ready tomorrow for any willing helpers...