One hacky solution to manipulating what pages are shown in the sidebar is to use the get_pages function, which returns a dictionary with strings as keys, and dictionaries containing details about that page. Once this initial page list is generated, it is cached, and you can manipulate it in order to change the list of pages shown in the sidebar. If you create a function which deletes any entries that you would not like to be shown, this will also remove them from the sidebar.
We are working on some changes that should make this easier in the future.