Oooh, I understand now what you are trying to achieve, but that won't work. You want AirDNS to tell No-IP your IP address but it's not the purpose of this feature.
What you really do with it is to give a name when forwarding a port and then you can reach your OpenVPN client by connecting to that name.airdns.org along with the port you forwarded (if it's port 9000, you connect to your client via name.airdns.org:9000). This is not a mask for DDNS domain names from other providers.