Add http header of Server IP address?

So you want to insert a header in the response with the IP address of the LTM pool member that served the request? That's a bit simpler:

when HTTP_RESPONSE {

    Replace (or insert if it doesn't exist) a custom HTTP header with the selected server IP and port
   HTTP::header replace my_custom_header "[IP::server_addr]:[TCP::server_port]"
}

The client will see this as well, so it should be present in the Fiddler trace.

Aaron