Those 2 options are only for automatic configuration. The router will use your account and download the config for you.

You can for any other service and custom servers (like you wanted to do in the other thread) just use the manual configuration. You paste the config that the server UI gave you when creating a new client.

Just remember to use your DDNS address instead of the IP in the client config, or else your clients will not be able to connect if your server IP changes.