You would need to setup what is known as split-DNS. You would likely need your own domain name for it to work correctly. Also on your internal network you would need a DNS server to resolve hostnames. Instead of using an IP address to connect, you would use a hostname (i.e. blynk.yourdomain.com). On your internal network, the host name would resolve to the internal IP of the blynk server. From the outside word, it would resolve to your public IP address assigned to your router. Using dynamic-dns services if fine but will not accomplish what you are trying to to do. They are only for assigning a host name to your IP and use that instead and no matter when your IP changes it will always resolve to your IP.
So once this is setup and working correctly, when you use blynk.yourdomain.com it will resolve to your internal IP when you are inside the LAN and resolve to your public IP when you are out and about in the world.