This looks closer to my setup with Apache mod_php, the idea being that Apache is essentially a wrapper for php and only called when needed. I would rather do this than have yet another link in the chain to fcgi etc.
I am using Nginx Proxy Cache Purge from http://wpselect.com/blog/wordpress-nginx-proxy-cache/ which purges the cache when you publish, update or comment and the plugin is quite a bit more complex. It needs nginx to be compiled with ngx_cache_purge.
Does your approach of modifying the X-Accel-Expires to zero do the same thing?
BTW as I run sites under group www-data, by putting the plugin into mu-plugins and setting ownership to nobody and ensuring no world read, the plugin cannot be seen let alone deactivated by any site admins!