I just updated this FAQ.  http://m0n0.ch/wall/docbook/faq-webGUI-from-WAN.html

The example shown will only work if you have a static public IP.  I'm
looking for a sanity check.  If your WAN is DHCP, you'll have to set
the destination to any, right?

For situations like this, maybe the destination should have WAN
interface address as an option in the drop down.  Or am I missing
something?

Thanks,
-Chris