Posting an update in can someone searches in the future. I've found a way to use US based credit cards including Amex to reload into the TnG e-wallet app.
Go on Lazada and after creating an account, buy the TnG reload pins, largest denomination is RM100. These pins can then be used to reload the e-wallet app. Max transaction for reload pins is RM1500 a month.
Another alternative is to reload the physical card itself at supermarkets that offer TnG reloading services but thats only if you use the physical card alot instead of the e-wallet app.