I go through this joy every month. It takes me an average of two large glasses of wine each time.
Sigh.
Two options, really:
1. Keep or open a US account, transfer money into it regularly and set up a direct debit. This will save you any additional fees.
2. Ring them every month, go through a bunch of stupid people who only have a script to work from and don't understand the concept of a foreign address, and pay by debit card. But don't tell them it's a debit card 'cause they'll tell you that you can't pay with a foreign debit card. Tell them it's a credit card. Trust me, it's easier just to tell them that. You have to pay an extra $10 a payment for the privilege of paying by card though....
Sigh.
ETA: I can't figure out how to pay online without a US account....
ETA2: I do think you can apply for a lower payment but I haven't tried it with them so not sure exactly how to do it.... I know with AES (who SUCK BEYOND SUCKINESS - far worse than Sallie Mae. Far, far worse) you fill out a form similar to the forebearance form....