Interesting... so it's sorta the opposite way that the Navigator window works.
Remember when Photoshop used to be able to open just a piece of a larger file? I don't know why that ability was ever taken out; I'm sure it had to do with silly legal mumbo-jumbo but back in the day when one had a gigabyte image and machines effectively maxed out around 2 gigs of RAM (if you were in a big shop!) that was a life-saver....oh yeah, it was called Live Edit.
So, sorry not really answering your questions but I wanted to give it some track.