Per domain real_ip_header

I'm not sure how good/bad idea this is, I'll describe my issue and maybe better solution will came up during discussion.

Configuration:
- Workflow 2.10
- EC2
- TCP ELB with proxy protocol
- Router deployment with `router.deis.io/nginx.useProxyProtocol: true` and proper `router.deis.io/nginx.proxyRealIpCidrs`.

Usually our request are running `client -> elb -> workflow` and it's working fine real ip is present in logs. However some domains (not even whole apps), are running through CloudFlare `client -> cf -> elb -> workflow` and here hell breaks loose :/ we're getting CF ip as remote address. So best option would be per domain `real_ip_header`, is it possible? Each domain is separate server block in nginx.conf, but is application/domain configuration available from nginx.conf template?

Maybe are there some workarounds? Switch to HTTP(S) LB is not an option.