synchronizing 2 heterogenous branches by cherry-pick

One of those weird real-world situations, advice appreciated:

Given... one Git repository with one branch "left" and one branch "right" both branches have a different history (common ancestor is 0000000) both branches have different content _however_, at one specific commit in the "left" and "right" branch it can be said that the content of specific subdirectories is identical these commits are marked with a tag "equal"

Thus, patches which only modify the identical content can always be applied without conflicts on both branches. I commit a new patch on "left", I can cherry-pick it to "right" and both trees are identical again.

Issues: Cheery-pick takes only one commit. I have to find commits by hand. Ideally, I want to specify equal..HEAD, if 10 commits are "left" and "right" are 7, well, then cherry pick the last 3 from "left" to "right". Note that the patch content is always identical, the commit text message (author/committer/timestamp/...) not always Note that ideally only one way synchronizing occurs. Bonus points if I can add on both sides and then start magic sync...

Any good idea on how to automagically script these cherry-picking?

Martin