You can not. You are probably talking about an NGINX + Apache setup, where NGINX only acts as a reverse proxy. In this case Apache still handles PHP and .htaccess files. That's not really true. Both NGINX and LiteSpeed can serve static files a LOT faster than Apache. If PHP or MySQL becomes the bottleneck in terms of resource consumption fully depends on the application. I've often seen applications which caused a lot higher PHP load than MySQL load.
Disable anything related to htaccess and directory lookups, youll see how fast apache will become. Most of its problems regarding speed comes from this. Nginx does not allow you to use htaccess files. That is of course not possible for virtual hosting - imagine : a guy will come and buy hosting to set up wordpress - or any other popular blog/forum/anything script - and voila - it doesnt work !! why ? because you cant do htaccess with nginx - have to contact administrator and have the htaccess rules added to server's httpd.conf .... there are important issues with nginx too. fragmentation etc.