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