x-forwarded-for and geoip

Hello, I use nginx as web server and have problem with visitors which use opera mini. Opera mini use transcoder and I always get ip of transcoder server instead of real visitor ip. But visitor ip is send with x-forwarded-for. This is not problem in php, I use function where try x-forwarded-for and if empty, use remote_addr. But what about geoip module? If I use "real_ip_header X-Forwarded-For;", then it work for opera mini and proxy visitors, but make problem for normal visitors. Is there any solution for real_ip_header to use x-forwarded-for only if it's not empty?