Is there any way to edit or add to the login page html/js?

The reason I ask is because my employer has sitewide navigation elements that we would like to add to the top of the login page -- particularly so that people who log out are not left at a dead end.

The html files added to a skin seem to only affect the Zimbra html once you have logged in (e.g. the main application UI).

If it is not easy or advisable to make a change like this, I won't attempt it... though in that case I would lodge a request to improve the skinnability of the login page!