Very interested to see if this strategy will work as this would negate the need to open a US checking account and also not having to pay 20USD every month using XE money transfers.My strategy for paying my ICC may help there - Citibank AU Global Currency Account denominated in USD, and a Revolut account. I have Revolut premium ($10/month) but if your bill is less than $9k USD then you can use the free account. Load your money to pay the bill onto Revolut, then use Revolut to convert it to USD (fee free) and then SWIFT it to your Citibank AU USD account, at which point you SWIFT it to Amex.
The reason for using Revolut is because Citi has a terrible exchange rate which is fine for like $10, but quickly loses you a lot of money as you increase the amount. The reason for using Citi is that Amex uses a "For Further Credit" account (the beneficiary is not the account holder) so you cannot use Transferwise, OFX, or any of those other providers - it must be a bank, and Citi allows you to hold the USD in USD until you need to send it, and send it free.