Exclude Piwik directory for Pagespeed in nginx

Because of this error I’ve heard that we have to deactivate Pagespeed to use Piwik.
Unfortunately the method which is described in the FAQ (How do I configure my server to let Piwik serve HTML files? - Analytics Platform - Matomo - url tag does not work here) doesn’t work:

pagespeed Disallow "*/piwik/*";

We’re using nginx with Plesk 12 and Piwik is installed in a directory on the main domain. So we’re not using a subdomain for Piwik Is this possibly the reason that it does not work?

German thread: 301 Moved Permanently