Actually, the manual correction is probably not only different for every miner out there based on their location, but also depends on how many other workers are currently connected to the various pools. It's probably a very unreliable method to determine a block finder.

Maybe it's possible to hook into bitcoind and see in which order connected nodes send the new block information. There might be patterns, but I suspect they are not very constant and need to be re-learned often. The learning would probably take a few hours at the begin of every session to recognize patterns of deepbit, BTC guild, and other pools, if there is any difference.