"[A]n author cannot grant a Creative Commons license in a pre-print
after having signed away all rights in the article in a publication
agreement."
Simple solution: Don't bother to use a CC license for your preprints or
postprints! Post your preprint claiming copyright in your own name, and
then go ahead and sign a copyright transfer agreement for the published
postprint if you want to or must.
There is absolutely no need or reason to assign users any more "usage
rights" than what already comes with the territory, in making the full
text (of either preprint or postprint) freely accessible on the web
(by self-archiving it).
(Of the over 9000 journals indexed by http://romeo.eprints.org/
93% already endorse self-archiving: 69% for the postprint plus 24% for
the preprint.)