I would like this in my Flex Viewer 2.1 too, I actually tried rewriting Roberts implemetation for the SFV 1.3 to the Flex Viewer 2.1. I managed to get rid of all errors, but when I ran the application there wasn't a map at all, all was blank, that's were I gave up.
It will need a lot more modifications than changing extent.containsExtent to extent.contains, to apply this to the FlexViewer 2.1 that's for sure 🙂