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.