fern I was looking at that also. I know paypal you can convert between usd/gbp etc. but that does us no good. even with bitcoin7 within there own markets euro/usd etc there is a bit of a spread.
The only way to do it as far as I can tell is to have a local account in each country that you want to trade currencies in. Then have a pool of cash in each, keep a record of your trades separately with your arbitrage calculations and then make your transfers periodically.
Of course you are exposing yourself to risks from currency fluctuations but USD/EUR/GBP is a good bit more stable than BTC so this should not be a huge problem in the short term at least.