be sure to know what you're doing, the steps write a custom Vhosts Template that gets parsed by plesk to generate the Vhost conf file for each Domain, the impact could be devastating ;)

first, copy original default nginxVirtualHost template to custom directory (as in [1], [2])

$ mkdir -p /usr/local/psa/admin/conf/templates/custom/domain/
$ cp /usr/local/psa/admin/conf/templates/default/domain/nginxDomainVirtualHost.php /usr/local/psa/admin/conf/templates/custom/domain/

edit the custom template to your liking

$ vi /usr/local/psa/admin/conf/templates/custom/domain/nginxDomainVirtualHost.php

search location that has 'nginxStaticExtensions' and add 3 lines to make it look like this:

   location ~ ^/(.*\.(<?php echo $VAR->domain->physicalHosting->proxySettings['nginxStaticExtensions'] ?>))$ {
        expires 30d;
        add_header Pragma public;
        add_header Cache-Control public;
        try_files $uri @fallback;
    }

then let plesk generate new domain configs

$ /usr/local/psa/admin/bin/httpdmng --reconfigure-all

optionally, verify the new conf has your additions

$  cat /var/www/vhosts/sampledomain.tld/conf/nginx.conf | grep 30d

$  curl -I -L -H 'Accept-Encoding: gzip,deflate' https://sampledomain.tld/pathto/a-stati-file.css

you should see 'Expires On' date in the response

from now on, for every filetype described in the plesk panel in the field 'Serve Static files through nginx' will get the cache headers, to tell the browser to keep them.

• [1] http://docs.plesk.com/en-US/12.5/advanced-administration-guide-linux/virtual-hosts-configuration/changing-virtual-hosts-settings-using-configuration-templates.68693/
• [2] http://docs.plesk.com/en-US/12.5/advanced-administration-guide-linux/appendix-b-configuration-templates-structure.68820/