Customizing Paypal Express's Review Page using ActiveMerchant

Question

I am using ActiveMerchant to give my rails app access to Paypal's Express Checkout. I would like to include the Order Details on the Review Page as described here: https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/e_howto_api_ECCustomizing

Can this be done?

Currently, my controller code looks like this:

def paypal
  #currently, options is unused, I'm not sure where to send this info
  options = { 
              :L_NAME0=>"Tickets", 
              :L_QTY0=>@payment.quantity, 
              :L_DESC0=>"Tickets for #{@payment.event_name}",
              :L_AMT0=>@payment.unit_price
            }

  #the actual code that gets used
  setup_response = gateway.setup_purchase(@payment.amount,
    :ip=> request.remote_ip,
    :return_url=> url_for(:action=>:confirm, :id=>@payment.id, :only_path=>false),
    :cancel_return_url => url_for(:action=>:show, :id=>@payment.id, :only_path=>false)
  )
  redirect_to gateway.redirect_url_for(setup_response.token)
end

If what I'm trying to do is possible, what do I need to change?