Problem after upgrade wit Domains served via google pagespeed service

[Brujo]

one of our Domains is served via google pagespeed service and this was working fine under Plesk 11.5.x but stopped working after upgrad to plesk 12.0.18

The failure which comes up in the Browser is: Fetching of original content failed with the following error: Proxy Publisher Failure - CONNECTION ERROR. If you own this domain, please consult this FAQ.

Google FAQ: I see the error "Fetching of original content failed due to Proxy Publisher Failure <Error Name>. If you own this domain, please consult this FAQ." when loading a page on my site. How do I fix this?
To fix this issue, please implement the X-Forwarded-For header. This error occurs when PSS cannot establish a stable connection with your origin server, likely because your origin server is now seeing a large number of requests coming from a small number of IP addresses (Google's servers).

to get it work under Plesk 11.x was to add in the nginx.conf in the http section the Google pagespeed real IPs & X-Forwarded-For, but with plesk 12.x it seems that this does not work anymore.

has anyone a hint for me how to solve