Active Admin : triggering a modal window from a click on an action_item link

I have that action_item on my admin page:

action_item :only => :index do
    link_to I18n.t('admin.dem_ref_nvl_etb'), :action => 'whatever'
  end

I'd like to know how I could display a pop-up window by clicking that link above, pretty much just like batch_action does when you use it with a "form" option (I don't need such an action here, it's just a basic link).

Any hint ?

Thanks a million for reading and helping!