Add WAN IP to hosts file?

[gem7]

I would like to have the current WAN IP included in the hosts file so that internal clients can determine it with a local DNS lookup (rather than depending on a DDNS provider).  I see that hosts I add in the HOST OVERRIDES section of the DNS FORWARDER configuration are added to the hosts file.  Is there some type of substitution macro/alias I could enter there for the WAN IP so that it always reflects the CURRENT WAN IP (regardless of source - STATIC,DHCP,PPPOE…)?  I would envision something like: 
host: wan  domain: mydomain.com  ip: %WANIP%

If not, does anybody know of a different approach?