Storing the slug as a custom field

I’m looking for a way to store the newsroom slug as a custom field. The headline extender is storing the post title correctly, but in GDocs, the newsroom uses slugs for the titles of the articles. I see some code in the extender about storing it, but it is getting lost. Storing it in a custom field is fine, I just want to maintain it in WP so that the editors, if they need to, can refer back to the original post.