Resurrecting this old thread because it has some potential. I use CurrencyFair to change money from GBP to Euros and can vouch that the service and system is excellent.
In my case I linked my UK bank account and my Euro bank account but I can add others like a USD account. I deposit GBP, offer for exchange to Euros and when thats done the money sits in my account as Euros. When I ask for it to be sent to my Euro bank account it costs 3Euros charges for any amount and arrives in a couple of days.
Maybe if I added an MT Gox bank account number the money would go straight to them in USD.
Opening an account with CurrencyFair requires that you provide full verifiable ID.