I was paying for checked luggage on GOL flight (the ticket being a TK issued award) and as you experienced they seemed to be requiring a Brazilian credit card (or at least, billing address). I just entered a random address and my US (Chase) Visa CC info. They processed the payment - which I believe was a charge for $18 BRL - and provided me a receipt for that amount but it charged my card $18 USD.

After my flight I called Chase to dispute the charge of dollars vs the BRL on their receipt and Chase just gave me a refund without, to my knowledge, taking the matter up with GOL.