Inline editing of foreign keys
I was wondering how easy it is to implement inline editing of module forms via a popup. For example, I have a module with
public $foreign_keys = array('imageID' => array('app' => 'images_model', 'order' => 'imageName asc'));
On the edit page, this gives me a dropdown box with  & [add] buttons. When I want to say, add a new option (for that dropdown), I click the button and I get a "create" page from the images_model.
How can get that "create" page to appear as a popup? It happens elsewhere, I'm not sure how that's implemented...