Lightbox Forms: Can we append custom HTML and why no prefill?

Although, this is on our website, and not LPs, but definitely a solid alternative.

OK, here's the code I'm using which is the same code I use on other pages, with the addition of the lightbox line. Are you saying that I want to replace the form.vals (or encapsulate it within) a whenReady()? Or is the problem that I'm showing the lightbox too early?

function showMainForm() {

  document.getElementById("form-div").innerHTML = document.getElementById("form-html").innerHTML;

    MktoForms2.loadForm("//app-sj02.marketo.com", "005-SHS-767", {{my.Form ID}},

      function(form) {

      MktoForms2.lightbox(form).show();

      form.vals({"web_capture_country":"{{lead.Web Capture Country}}",

        "Phone":"{{lead.Phone Number}}",

                 "FirstName":"{{lead.First Name}}",

                 "LastName":"{{lead.Last Name}}",

                 "Company":"{{company.Company Name}}",

                 "Email":"{{lead.Email Address}}",

                 "City":"{{lead.City}}",

                 "web_capture_state":"{{lead.Web Capture State}}",

                 "Title":"{{lead.Job Title}}",  

                 "PostalCode":"{{lead.Postal Code}}",

                 "Address":"{{lead.Address}}",

                 "form_product_interest":getFPI(),

                 "formProgramID": getCampID(),

                 "flexField1": getDPI(),

          "facility_type":"{{lead.Facility Type}}"

                });

      var formEl = form.getFormElem()[0];

  MktoForms2.whenReady(function(form){

     document.getElementById("mktoForm_{{my.Form ID}}").setAttribute("autocomplete","on");

     document.getElementById("Email").setAttribute("autocomplete","email");

      document.getElementById("Phone").setAttribute("autocomplete","tel");

      document.getElementById("FirstName").setAttribute("autocomplete","given-name");

      document.getElementById("LastName").setAttribute("autocomplete","family-name");

      document.getElementById("Company").setAttribute("autocomplete","organization");

      document.getElementById("City").setAttribute("autocomplete","address-level2");

      document.getElementById("web_capture_state").setAttribute("autocomplete","address-level1");

      document.getElementById("Title").setAttribute("autocomplete","organization-title");

      document.getElementById("PostalCode").setAttribute("autocomplete","postal-code");

      document.getElementById("Address").setAttribute("autocomplete","street-address");

        });     

      form.onSuccess(function() {

          window.location.assign(LinkURL);

    return false;

      });

    });

  }