_edit_multi.haml

#attached_files
  %p.declaration
    Attachments:
    %em 
      = add_object_link("add", "#attached_files", {:partial => '/attached_files/file', :locals => {:form => form}})
  - object.attached_files.each_with_index do |attachment, i|
    = render :partial => '/attached_files/file', :locals => {:form => form, :attached_file => attachment, :child_index => i}

_file.haml

- attached_file ||= AttachedFile.new
%p.attached_file
  - if attached_file.new_record?
    = form.fields_for 'attached_files_attributes[]', attached_file do |fca|
      = fca.file_field :attachment
      = fca.hidden_field :nested, :value => true
      = link_to_function 'remove', %{jQuery(this).parent('.attached_file').remove();}
  - else
    = link_to attached_file.name, attached_file.url

template_helper.rb

def add_object_link(text, where, render_opts)
  html = render(render_opts)
  link_to_function text, %{var html = jQuery(#{html.to_json});html.appendTo(jQuery(#{where.to_json}));}
end