Add custom link to submit button

We're working with an event registration vendor to set up a webinar. The vendor sent us a long link with that includes query string parameters, and said to do this:

• Please use the url below to pass through user info via POST from your registration form. Since you are not sending a Password value, please send the one prepopulated below for all users.

One of the parameters is a password that they included, and other parameters include first name, last name, email, and a few other fields in the Marketo registration form. My question is, how can we/where do we add this link to our form? I'm assuming I would write something in an html box on the landing page itself, since it doesn't appear to be a place to do that in Forms 2.0...

I'd greatly appreciate any guidance anyone can give on this! I'm not a programmer, but I can code...