Passing tar(1) options via git-archive(1)

Some background from the git-archive(1) man page:

    git-archive behaves differently when given a tree ID versus when
    given a commit ID or tag ID.  In the first case the current time is
    used as the modification time of each file in the archive.  In the
    latter case the commit time as recorded in the referenced commit
    object is used instead.

Would it make sense to add an --mtime option to git-archive(1) to enable explicitly setting the mtime for all files in the archive? It could just pass through to the tar(1) --mtime option.

My use case is `git archive HEAD | docker build -`, in which the Docker cache is prevented from working because the mtime keeps getting bumped on all files. I would like to have the mtime always be the same.

See, e.g., <https://github.com/deis/deis/issues/1334>.

Otherwise, how about a generic way to pass options to tar(1)?

Thanks, Daniel