The only way I can theoretically think of doing that is loading the page via iframe and have javascript manipulate DOM, but... that's all theory. Unless the lander allows you to pre-populate fields by reading the GET data - like this query:
www.example.com/form.cgi?field1=data1&field2=data2
Or using the POST method to push data, you are going to find it rather difficult. Maybe it's possible with iframe though, that's where I would start investigating if I were you.
A Google search lead me to this:
jQuery/JavaScript: accessing contents of an iframe - Stack Overflow
then this:
simple » Blog Archive » How to access iframe in jQuery
Looks like you might run into a 'Same-origin Policy' (
Same-origin policy - Wikipedia, the free encyclopedia), which might deny you further. There is a workaround:
"To enable developers to, in a controlled manner, circumvent the same-origin policy, a number of "hacks" such as using the fragment identifier or the window.name property have been used to pass data between documents residing in different domains. With the HTML5 standard, a method was formalized for this: the postMessage interface, which is only available on recent browsers. JSONP can also be used to enable Ajax-like calls to other domains."
If you can accomplish this feat, you can sell this technique and bank hard, cause it's rather difficult but can be very useful, but has the potential to be a HUGE security risk.
Good luck bro.