Post Render Cache

This module allows post processing of render arrays just after them
being retrieved from cache. It allows you to apply small per-user modifications
on globally cached output, without having to resort to per-user caching.

Think of it as a poor man's ESI, or the same thing than #post_render callbacks,
except they will run at drupal_process_attached() time at initial rendering
and after drupal_render_cache_get().