Commit ID in exported Tar Ball

Hello,
Michae, a friend of mine, is in the phase of migrating from git to cvs.
He releases tar balls of his software project using gitweb. He would
love to have a way to have the commit-id of HEAD of the export contained
in one of the files he exported that way. Is there infrastructure in git
that makes that already possible or does he need to some kind of
gerneration tool by himself? Maybe it would be helpful if the
git-tar-tree would generate a file .commitid or something like that in
the generated tar tree.

        Thomas