Nginx - How to serve 404 and static files through private networking?

I’ve followed this tutorial exactly to set up, successfully my Node.Js app: https://www.digitalocean.com/community/tutorials/how-to-set-up-a-node-js-application-for-production-on-ubuntu-14-04

My Node app lives on a separate droplet, as does my Nginx. I’m redirecting all my www and http traffic to https://domain.com. This all WORKS.

Now I also want to serve custom error files. But they are located in the node app on the other droplet, in the public folder /var/www/app/public. Is there anyway I can serve my 404 file from Nginx, but keep it on the Node.JS droplet?

Same question for my static files (images/fonts), is there a way I can serve my static files from Nginx, but keep them on my Node.js droplet (NOT copy them over to Nginx droplet?)

Thanks

server {
        listen 80;
        server_name www.domain.com;
        return 301 https://domain.com$request_uri;
}

server {
        listen 443 ssl;
        server_name www.domain.com;

        return 301 https://domain.com$request_uri;

        ssl_certificate /etc/nginx/ssl/www.domain.com.chained.crt;
        ssl_certificate_key /etc/nginx/ssl/www.domain.com.key;
        ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
        ssl_ciphers AES256+EECDH:AES256+EDH:!aNULL;
        ssl_prefer_server_ciphers on;
}

server {
        listen 443 ssl;
        server_name domain.com;

        ssl_certificate /etc/nginx/ssl/www.domain.com.chained.crt;
        ssl_certificate_key /etc/nginx/ssl/www.domain.com.key;

        ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
        ssl_ciphers AES256+EECDH:AES256+EDH:!aNULL;
        ssl_prefer_server_ciphers on;

        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

        location / {
                proxy_pass http://ip_of_node_droplet:4000;
                proxy_redirect off;
                proxy_http_version 1.1;
}
}