For reference, BIP 10 is what I use in Armory to do the same thing.  It was intended to be an ASCII-based way to move all this data in "blocks", either through email or text files on USB.  It does work (Armory has been using it for offline transactions for 2 years), but it will be replaced soon.  I'm told the payment protocol can replace this, but I still haven't had much time to dig into the payment protocol...

Of course, that dramatically increases the complexity of it, having to pass around potentially MB of supporting transactions to verify those 8-byte values.  Can the payment protocol handle it?