The information I had found on the now out of reach Green Pirate site may be viewed
here
Though a bit less clear than on Green Pirate, it is quite understandable and usable under Linux and doesn't require any Calibre plugin.
A very very useful tutorial for Linux-and-Kobo users.
EDIT Note this and others recent posts of mine on this thread concern KOBO - not Kindle or any other reader - and books with Kepub format.