This is actually pretty easy to do with "git rebase -i". Not ideal, but definitely workable, especially if you only occasionally want to generate patches. For example, take this ensure-dir-only patch: http://pastie.caboo.se/159593. I generated that by creating a new branch copying stable, running "git rebase -i official", and squashing all the related commits together, leaving a set of almost orthogonal commits (almost because ensure-dir and date both depend on $).
I'm not entirely sure what use you had in mind, so this may not be a great solution. It doesn't take into account dependency-tracking at all. But we could easily make a "patches" branch which would just be a rebased version of stable, although we'd have to keep it updated and rebased, and the constant rebasing would mean that pulling from it might get a bit nasty.
