So technically, what you’re looking for can be achieved. The biggest challenge is that you’re looking to collect sensitive password data, and since Unbounce doesn’t have support for SSL just yet, we strongly advise against collecting this data as it will be stored in plain text in our DB. As an alternative, you can embed a solution from 123ContactForm, which not only offers obscured password forms, but can store data securely in their DB.
However, I’d like to highlight another thought I had about this situation. At our core, Unbounce was developed as a landing page builder. Sometimes, registration pages aren’t necessarily a great spot to land when coming from Paid Media, SocMed, Search, etc. With that being said, it might be worth building a few landing pages which highlight your features and unique value propositions, and segmenting some of your traffic towards them, with the CTA leading them to click through and register. That way you can simply redesign your registration page on your own site once, and instead focus on highlighting your value propositions to educate your potential customers before they register.
Just a thought, but I’d be curious to hear what you (or other members of the community) think about this approach.