There is! Make sure you are on the latest version of SmartBuilder (Help > About SmartBuilder ... should be version 4.3.1). If so, then you can go to Edit > Lesson Settings, and uncheck the value that says "Use the same height for all pages" and press OK.
Now on each page you'll notice a ruler along the left edge, and at the bottom of the page is a gold guideline with an arrow. You can drag that arrow up and down to alter the size of that particular page.
Here's a video that shows the process in action - https://www.screencast.com/t/rs87mgAkcn6
Hope that helps!