A little workaroundsy, but how about this:
-) Create a new scene in hype which contains a full screen button. This scene is the first scene of the hype project.
-) Set "on scene load" of this new scene to "jump to scene -> next scene"
-) Export your widget and include it in iBooks author.
-) Remove title, caption, background and position on page. The button of your first scene will be shown. Set to "play full-screen".
-) When you click on the button (you're actually clicking the widget, but your fullscreen button on the first scene looks like a button), ibooks will play the widget full-screen. The on scene load we set will immediately load the second scene - your actual content.
widgettest.hype.zip (32.1 KB)
widgettest.iba.zip (336.1 KB)