ADMIN AREA: Show draft posts in 'page parent' dropdown in page attributes

Background: I have built a relatively complex WP site for a client which is more of a CMS than a blog and relies on a hierarchy of pages being built. (Well, they’re actually custom post types with 'hierarchical' => true set)

My question: is it possible to show draft (or pending review) pages in the page attributes ‘Parent page’ dropdown list? Without this, it means making each page live before the whole section is ready – and that’s not a suitable solution.

What I’ve tried:

• Looking for an action which gets called to build the list (can’t find one)
• Looking in the source code for where the list is created (it’s built with wp_dropdown_pages which doesn’t appear to let you choose the post status)

Any suggestions? If the worst comes to the worst, then I suppose that I’ll have to hack WP core – but that’s obviously far from ideal and I absolutely don’t want to do it!