It may depend on the loan servicing company. Mine's through Sallie Mae, and there's no way to set up any kind of online payment-- one-off or recurring-- from anything other than a U.S. checking account. I can't even just pay online with my Visa debit card.
While I do still have my old credit union checking account, I find the idea of having to remember to transfer a certain amount of money, by a certain time each month (and paying the transfer fees), a recipe for loan default. So I just pay with my Visa over the phone each month. It's a very small amount anyway, so the foreign transaction fee (1%, I think?) is just pennies. I've got free U.S. calling, so the only thing it costs is time and sanity.
I'm still not sure why, if they're able to take Visa payments over the phone, they can't take them online as well. But oh well.
As a side-note, anyone who hasn't looked into the Income-Based Repayment plan should check it out. My monthly payment went from $420, to $20.