Programmatically render Page Manager page

/**
 * Implements hook_menu().
 */
function sample_module_menu() {
  return array(
    'render/user/%/page' => array(
      'title' => 'Member Profile Preview',
      'access callback' => true,
      'page callback' => 'sample_module_render_page',
      'page arguments' => array(2),
    ),
  );
}
 
/**
 * The menu entry callback for render/user/%/page.
 *
 * @param $target_uid
 * @return array
 */
function sample_module_render_page($target_uid) {
 
  module_load_include('inc', 'ctools', 'page_manager/plugins/tasks/page');
  module_load_include('inc', 'ctools', 'includes/context');
 
  $subtask_id = 'page_variant_machine_name';
  $page = page_manager_page_load($subtask_id);
  $task = page_manager_get_task($page->task);
  $subtask = page_manager_get_task_subtask($task, $subtask_id);
 
 
  $user_context = ctools_context_create('entity:user', user_load($target_uid));
  $user_context->id = 'argument_entity_id:user_1';
  $user_context->original_argument = $user_context->argument;
  $user_context->identifier = "User";
  $user_context->keyword = "user";
 
  // Turn the contexts into a properly keyed array.
  $contexts = array($user_context->id => $user_context);
  $args = array($target_uid);
 
  ctools_include('context-task-handler');
  $output = ctools_context_handler_render($task, $subtask, $contexts, $args);
  if ($output === FALSE) {
    return MENU_NOT_FOUND;
  }
 
  return $output;
}