There is a way to do it: just use ddclient!

ddclient does not check the ip address of the interface but calls a website which shows the ip address assigned by the provider to the router - so if this one changes ddclient updates the e.g. dyndns.org address.

Hint: do not run ddclient as a daemon since I made the experience that it crashes from time to time.
Better have it called by cron every 5 minutes...

techno.kid