The key pieces to study are:
In Simple.html, look for
In ViewController, look at
rectForElement, which will tell you where the item is in view coordinates, and
insertCustomView which actually builds the view and inserts it. Almost all of that method is just creating the view, the key pieces is the last line
With those, you can insert your view directly into the scrollview and it should be at the right place and the right size and you can even interact with it.
I assume you could use a similar approach without injecting an extra DIV just by asking for the
getBoundingClientRect() for the body element.