Is there a plugin to make non-linear items linear?

Is there a plugin to make non-linear items linear? And possibly to mark both the titlepage.xhtml and the cover image file as the cover image?

This would help to prevent the cover image from being duplicated during conversion (resulting in a broken image in the second cover image page) -- and from having to edit books to remove the page that has a broken image and to fix the non-linear error that Calibre always finds.

Thank you.