Hi Colin
This is a fairly standard feature when you use either the Relative Page Layout action or simply create your website using the inline box model - which i personally prefer.
In the link you provided, all the text is on the page is enlarged when the text display size is changed and not just the text within the ‘body’ section. The page then ‘expands’ to allow for the growing content. This is what will happen in your Freeway pages if you construct them in the methods i mentioned above.
You can probably search this forum for tips on inline box model construction.
Dan Jasker had some great videos explaining all this - and thats how i learnt it - but perhaps some of the others here know of a great tutorial for you.