Track Custom Proxy Headers, more than only X-Forwarded-For (no replies)

Dear Community,

unfortuantely i couldn't find a solution for tracking custom proxy headers, which the piwik-server receives. X-Forwarded-For is tracking Piwik by default, but wat is with custom proxy headers like X-USERNAME_PROXY_CLIENT, how can piwik track this?

Please help,
Many thanks in advance
elysium