Well I am not sure about the software and if it can use the WAN port, but it's definatly there. I will check when I am next at work to see if you can configure the WAN with an IP address / PPPoE etc... I suspect there probably isn't anything in the Woosh UI to configure the WAN port. But you could try sshing to the box and see if you can configure ETH0 / ETH1.
In theory you could take the open source code and then re-compile it and reflash the router... but I am not sure how easy that would be as I know from past experience the router providers have been coy about provding the tools to actually create the images.
I know the Broadcom based routers (Linksys WRT54G etc) have a firmware modification kit which allow you to take the firmware, open it up and make the changes you want such as to the UI etc, then re-compress the image for upload.