Make a form result display in a div on the same page

I will like to display the form result(submit the form to itself, wrapped in a hidden div) within the block itself(as well as the same page), instead of it redirecting to something like node/%webform/done?sid=?.

I tried overriding the hook_form_alter or hook_form_FORM_ID_alter, but it seems these functions cannot be overriden in the theme level, unless it is implemented by another module.

In my implementation anyway, I tried using the AHAH form type, so that the path attribute calls the drupal_get_destination() function, and the wrapper attribute updates a div.

function custommodule_webform_client_form_alter(&$form, &$form_state) {
if($form_id == 'webform_client_form') {
$form['wrapper'] = array(
'#prefix' => '<div id=feedback-result',
'#suffux' => '</div>',
);

$form['wrapper'] += _webform_confirmation($node);

$form['#submit'] = array(
                          'ahah' => array(
                          'path' => drupal_get_destination(),
                          'wrapper' => 'feedback-result',
                          'method' => 'replace',
                          'effect' => 'fade',
                          'event' => 'click'
                              ),
                          );

}
}

Thanks. Will be checking this post from time to time.