Passing a form object to a partial within a fields_for using observe_field

I'm a Rails newbie, so please bear with me. I'm using version 3.0.0.

I have a form to create and update articles which uses a fields_for to
nest a 'collaborator' resource, of which an article :has_many. I
would like for users to be able to search for other users to add as
collaborators (co-authors of the article) using a live search field
linked to a select box (or something similar).

Unfortunately, I need to pass the original article form object to the
search results partial on every AJAX request in the live search. Is
there any simple way to do this, or a better approach entirely?

Here's my code:

Following the nested model Railscast, my articles form includes this
div:

  <div class="article_form_collaborators">
  <%= f.fields_for :collaborations do |builder| %>
    <%= render 'collaboration_fields', :f => builder %>
  <% end %>
  </div>
  <p><%= link_to_add_fields "Add another collaborator",
f, :collaborations %></p>

The collaboration_fields partial includes an observe_field (obtrusive
as it may be...) call to handle the live search functionality:

<div class="collaborator_fields">
  Search for collaborator: <input type="text"
id="live_user_search_form" name="search" />
  <span id="live_search_results">
    <%= render :partial => 'live_search' %>
  </span>
  <img id="spinner" src="/images/spinner.gif" style="display: none;" /

  <%= link_to_remove_fields "Remove collaborator", f %>
</div>
<%= observe_field "live_user_search_form",
    :url => { :controller => 'articles', :action => 'live_search' },
    :frequency => 0.5,
    :update => 'live_search_results',
    :with => "'search_text=' + escape(value)",
    :loading =>
"document.getElementById('spinner').style.display='inline'",
    :loaded => "document.getElementById('spinner').style.display='none'"
%>

And the live_search partial just allows the user to select from the
search results:

<% if @live_search_users && @live_search_users.hits.count > 0 %>
  <%= f.select :collaborator_id,
    @live_search_users.hits.map { |hit| ["#{hit.instance.first_name}
#{hit.instance.last_name} (#{hit.instance.email})",
hit.instance.id] }, { :include_blank => true } %>
<% else %>
  <%= f.select :collaborator_id,
    current_user.friends.map { |hit| ["#{hit.first_name}
#{hit.last_name} (#{hit.email})", hit.id] }, { :include_blank =>
true } %>
<% end %>

The searching is handled through a live_search function in the
articles controller:

def live_search
    if request.xhr?
      if params['search_text'].strip.length > 0
        terms = params['search_text'].split.collect do |word|
          "%#{word.downcase}"
        end
        @live_search_users = Sunspot.search( User ) do
          keywords terms
        end
        render :partial => '/articles/live_search'
      else
        render :partial => '/articles/live_search'
      end
    end
  end

As you can see the live_search partial requires the article form, f,
for the select function, but obviously that's not available unless
passed somehow. I've tried passing it around using :locals in every
place I can think of, such as from the observe_field call through the
controller and back to the partial, but nothing seems to work.

Any help or guidance would be greatly appreciated!