Embedded Google Viewer - How to disable full-screen option?

Question

I use Google Viewer as embedded PDF-Viewer in a Web-App (PhoneGap). My Problem is, that when I open a PDF-File on an iPad and enter full screen mode, there is no way to get back anymore, because there is no "back"-Button like on Android devices. So I'd like to disable the option, to access full screen mode.

This is my code:

        <iframe 
            src="http://docs.google.com/viewer?url=http://www.physik.uni-wuerzburg.de/fileadmin/tp3/ThermoEDynamik/Uebungen/aufgabe29_31.pdf&embedded=true" 
            width="750" 
            height="1125" 
            style="border: none">
        </iframe>

I thought there must be an option like width and height just for full-screen mode.

Thanks for your help!