Drupal 7, define header/footer/... for your view programatically.

my_module.module

<?php

/**
 * Implements hook_views_data().
 */
function MYMODULE_views_data() {
  $data = array();
  
  $data[' MYMODULE__global']['table']['group'] = t('My Module');
  $data[' MYMODULE__global']['table']['join'] = array(
    '#global' => array(),
  );
  $data[' MYMODULE__global']['property'] = array(
    'title' => t('My Module extras'),
    'help' => t('Displays extra cats on your view!'),
    'area' => array(
      'handler' => 'MY_MODULE_views_handler_area_cats',
    ),
  );

  return $data;
}

/**
 * @inheritdoc views_handler_area
 */
class MY_MODULE_views_handler_area_cats extends views_handler_area {
  public function render($empty = FALSE) {
    return theme('MY_MODULE_display_more_cats');
  }
}