Pages: individual logfile per subdomain

I am running Gitlab Omnibus on a dedicated server with Pages activated on and several Jekyll Pages on I would like to use Piwik’s log analytics to monitor usage of those pages.

Unfortunately I found that requests to all those pages are being logged in a single logfile at /var/log/gitlab/nginx/gitlab_pages_access.log due to this setting in gitlab.rb:

pages_nginx['log_directory'] = "/var/log/gitlab/nginx/"

I have tried to set it to

pages_nginx['log_directory'] = "/var/log/gitlab/nginx/#{node['fqdn']}/"

but that caused nginx and mattermost to stay down after gitlab-ctl reconfigure.

So I am wondering how I can have individual logfiles for all my subdomains so that I can track them in Piwik separately. Any ideas?