Hi Ben - You could place the form on a separate page and display the form page in a lightbox. Take a look at our support article on using a button to open a lightbox webpage: 

http://documentation.unbounce.com/hc/en-us/articles/203805714-Adding-and-Editing-Buttons-and-Confirm…

Looks like this link isn’t working any more - just takes me to the home page of documentation. Can you please provide the correct link? 

Hi Jonathan, 

Yes, the link leads to the old support articles. 

Here is the correct one: http://documentation.unbounce.com/hc/en-us/articles/203805714-Adding-and-Editing-Buttons-and-Confirm…

Thanks Hristian! I’ll update Johnny’s post above. We had a few changes to our documentation this year and not all of the redirects have taken place. Sorry about that!

Jonathan, I would also check this thread out as well, as we’ve been chatting about this recently:

/topics/fancy-box-form-opening-new-page-in-the-lightbox

UPDATE: 

We’ve released a new feature into beta that allows you to build/launch your lightboxes directly within the page builder itself. This new release will allow you to add images, videos and even forms into your lightbox, and _it will allow you to attribute the lead/conversion back to the original page. 

Go check it out and sign up for the beta  here .