Producing tar file with 666/777 permissions

Dear GIT people,

How do I package a git repository in a tar file with 666 and 777
embedded permissions?  There's evidently some way to do it because the
Linux kernel source packages have 666 and 777 embedded permissions, but
git-tar-tree gives me a tar file with 644 and 755 permissions and
there's no obvious way to tell it to do otherwise.

There was lots of discussion on the mailing list about what permissions
to preserve when copying in and out of repositories (I obviously side
with those who want a single execute bit), but I could not find any
mention of permission issues in reference to git-tar-tree.

Please reply to me as I am off-list.
-- 
Matt McCutchen
hashproduct@verizon.net
http://hashproduct.metaesthetics.net/