Add code to page content

Hi, all. Could anybody tell what is the most appropriate way to append some content to a "nodeless" page? For example, when a module uses the drupal_get_form() function as a page callback to display some form, no $node object is usually created. Instead, the form output is immediately embedded into the page content and is drawn as is.
The only way I see is implementation of the hook_preprocess_page() function in my own module. Something like that:

function MODULE_preprocess_page(&$vars) {
  // ...
  $vars['content'] .= '<div>some code goes here</div>';
}

In other words, some piece of code is appended directly to the $content variable of the page.tpl.php template. Is there another way to achieve such a purpose properly?