I have not tested this out yet but it seems like appending the form data to the “Step 2” Unbounce landing page would require either a second custom Facebook tab or you would have to take the user out of the Facebook platform.  Any workarounds to keep the user inside of the custom tab beyond just eliminating the “Step 2” and putting it on the initial form?  You know what they say,

Curiosity killed the Facebook marketing campaign… Thanks for your help and insights!