So as I see it, bitcoin does nothing BUT hash checks. Each block it hashes is stored in the blockchain.

So all we would need to do is simulate those hashes in an internal network, then use one of those pc's to BUY using external scource, ie, the shop., placing hashes found on an internal network to the external blockchain, which of course, knows nothing of the internal network, and dont care, since the hashes created by the internal network were confirmed by other pc's on the internal network which were just as 'legal' as the external.. Just another theory

Edit: You read it here first lol..