Hi,
Please ignore my previous attempt at a patch. The code I thought was running did not because it was protected by an application_id not None check that had to be worked around.
I created a new patch to metadata/zip.py that I tested and it does do what I wanted.
As requested I have created a bug tracker issue with the patch attached.
http://bugs.calibre-ebook.com/ticket/8066
Thanks again for all of your help.
KevinH