no, you cant change the size of a web viewer dynamically. In your case, you only can fix it to the "more than one page" size. No, the scroll bars can not be hidden. ONly the status bar can be hidden.
A little trick would be to make two ore more layouts with the web viewer in different sizes, you self must decide if this is an option for you.
Everybody who knows better, please post!
Greetings from germany