Update Cart button ecommerce module

I want to be able to alter the name of the update cart element of the ecommerce shopping basket. I can do this but it breaks the processing of the update function since it is expecting 'update cart' as the value in $form_values['op']

function cart_view_form_submit($form_id, $form_values) {
  switch($form_values['op']) {
    case t('Update Cart'):
      cache_clear_all();
      cart_update_item_object((object)$form_values);
      return 'cart/view';

    case t('Checkout'):
      // force it not to validate so we see the update quantity page again.
      return 'cart/checkout';
  }
}

Does anyone know a way of putting this functionality into the template.php or otherwise to override the cart_view_form_submit function so that it can have a different text?