I know ther are many closed issues like #823, #759, #289.

But, I found It's possible ngx_stream_proxy_module.

especiaaly below.

stream {
    upstream ssh {
        server 192.168.1.12:22;
    }
        server {
        listen        12345;
        proxy_pass    ssh;
    }
}

how could I apply that on current installd nginx-proxy image?

heres stackoverflow
https://stackoverflow.com/questions/31324981/how-to-access-host-port-from-docker-container
heres nginx stream proxy module
http://nginx.org/en/docs/stream/ngx_stream_proxy_module.html