May be this is possible if you want to start the book as an application. If you talk about starting fullscreen mode in browser when the page is loaded, well this is impossible due to the Adobe company security policy. Flash player can be launched in full screen mode in browser only on mouse or keyboars event.
I wanted this option too, this is why I'm working on a custom button, which should appear in the center of the book righ after the book is loaded, and when clicked, would start the fullscreen mode.