If I am understanding your questions correctly couldn't simply utilizing rel canonical to allow you to sleep better at night?
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=139394
Also this is a pretty new feature out of Google that you might find interesting
http://googlewebmastercentral.blogspot.co.uk/2013/04/x-default-hreflang-for-international-pages.html