Dynamic IP from modem?

Device: NH20A

The rather short lease on dynamic IPs would not be an issue except the hub appears to have no way to retrieve the current IP address, and the only option for Dynamic DNS is a commercial service provider - I run my own DNS, tyvm. Yes, I could hack something using dig, or screen scrape whatismyip.org, or some equally brittle solution, but maybe someone knows if the router has an api which makes this data accessible within the LAN?