Hacking incremental rewrites of repositories, sparse in both history and files

I'm facing the challenge to migrate https://github.com/mozilla-b2g/gaia into http://git.mozilla.org/?p=releases/l10n/en-US/gaia.git. Leave out useless commands, filter on a set of files, rename and rewrite.

There's a pretty sane algorithm behind this, but I could use all the help to automate it, and to make it run incrementally as the branches inside the gaia repo evolve.
