This is what happens when you stand on the shoulders of giants - you don't quite know what you are doing, at least in my case.
I've been working on a way to dynamically load images into a Flex app and set them as the tiled background of a Canvas component. Luckily I spotted creacog's work which I adapted a little bit for my needs. You can see the results here.
So far the image loading and displaying as a borderskin of the Canvas works, but as you can see when you drag the box around is that as soon as scrollbars appear the image is no longer rendered and the Canvas's background color it displayed instead.
Feel free to use and reuse this code if you find it useful, and remember to credit creacog.co.uk who has done the hard work on this.