Adding files to a git-archive when it is generated, and whats the best way to find out what branch a commit is on?

I was wondering if anybody had any suggestions on a sane way to add a file to a git-archive when it is being produced.

For instance build procedures that expect to be run inside of a git WD wont work if built from an archived version of the tree. Being able to provide a file of additional data to the archive package would be a very convenient way to work around this.

Ideally id like to be able to specify a set of additional files to include in the archive as part of the git-archive command line interface, but I'd be nearly as a happy with almost any solution other than the one I came up with, which is to use archive to generate a tar file, then use tar to append the additional files to the tar, and then compress it. This process turns out to be quite slow in comparison to producing a compressed archive directly from git-archive.

Another question is whether anyone has any advice on the best way to find out the "best" branch an arbitrary commit is on. Where best can be flexibly definied to handle commits that are reachable from multiple branches. I have hacked a solution involving git-log and grep, but it performs quite poorly. I was wondering if there is a better solution.

cheers, Yves