I\'ve found many related questions but none with an answer that explains how to scroll an iframe using the 2 finger method in iOS 4.
I am able to scroll
A simple idea posted by rossb @ github.com/fancyapps worked beautifully for both scrolling in iOS 4 (2 fingers) and iOS 5 (1 finger) and solves the "blank content on scroll" issues that iOS 5's iframes seem to be plagued with. Basically, you don't want the iframe to handle any scrolling. Give it a fixed width/height and wrap the scrollable content in your included file in a div that can be scrolled.
Here's an example:
a-file.html:
...all my normal content...