How to make the router think I'm where I'm not?

I currently live in japan but have an English xbox with an English Call of Duty: Black Ops, but can't play the new maps because of the region coding. I know there is a way to make it so the xbox thinks I'm in the states and I can download and play the new maps i just have no idea how. my router is a cisco WRT54G2 V1.5.