You can now add your PASMO to your Apple wallet and fill it up with an US Credit card. As of today this will save you 33% due to the currency exchange rate. I’m guessing this will also work with credit cards from other countries. Just make sure your card does not have foreign transaction fees.
Update 10/22: For some reason house PASMO no longer works with Visa or MasterCard but SUICA does work with MasterCard.