Another possibility would be to checkout the tag that you want to use and patch it.
I patched 4.2.8.Final and it needed only 3 little changes. I am awaiting the approval of my boss regarding the javassist update, so maybe I have to build hibernate myself too.
I will let you know when I do that and post links to a repository that contains patched versions.
I also sent you an email regarding the migration, hope you can give me some info.