You can run Isso on the same domain as your website, which circumvents issues originating from CORS. Also, privacy-protecting browser addons such as Request Policy wont block comments.

server {
    listen       [::]:80;
    listen       [::]:443 ssl;
    server_name  example.tld;
    root         /var/www/example.tld;

    location /isso {
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Script-Name /isso;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_pass http://localhost:8080;

Now, the website integration is just as described in Quickstart but with a different location.