As you might already noticed in article you linked, presenting bank's page in iframe is a preferred option. Although if you read in further, it presents other security features, specifically in regard to phishing protection. Because your client won't know to whom is he really sending his password.
But going back to your proposition, if you present it in iframe or popup window, you would be able to store the original form on your base page and then resubmit it with received authentication token. It's a very good idea because you would not need to do any PCI compliance stuff. So not only it's easier for you it is recommended :).