id of new object dynamically created in a nested form

In my nested form I have a link to open a popup with selections. When
a selection is made, the popup closes and the selection is added to a
text box.

Because I have objects that can be dynamically created in the form I
can't just use the id of the object to assign the selection to the
input text box.

I have this in my view

  <td><%= f.text_field :couchetype, :readonly=>true%></td>
   <td><%=
link_to( image_tag('more.png', :border=>0, :id=>"sample_sample"),
{:controller=>"thesaurus", :action=>"list"}, { :popup=>['thesaurus',
'height=800,width=400,location=no,scrollbars=yes']}) %>
   </td>
</tr>

and then this in the popup

function copyData(id,value){
    var el = window.opener.document.getElementById(id);
    if (!el.value)
       el.value = value;
    else
       el.value = el.value + "; " + value;
    this.close();
}

I want to send the id of the new object to the popup so that I can
refind the text box to assign the selections. How can I do that?