But that's hardly a "FOOM", and the Romans would have a hundred years to stop you,

Exactly. And here the parable breaks down. The upload just might have those centuries. Virtual subjective time of thousands of years to devise a cunning plan, before we the humans even discuss their advantage. Yudkowsky has wrote a short story about this. http://lesswrong.com/lw/qk/that_alien_message/