Contact eBay and say you bought your friends business and want to transfer ownership of the account to him. If they say you can't, ask to speak to CSR in the United States and ask the same question to them. You will be asked to fax something in, and then it will all be legit.
If you want to be less legit, change the phone number, wait a month and change the address, and then change CC details a month after that. Changing a lot of information too soon will raise some red flags.