Xively has a heap of APIs so you can access your feed data in other ways rather than just loading up the web page. I was able to use their sample code to put together a simple iOS app that lets me check the temperature and light levels in my study at any time, from anywhere. It’s nothing fancy but a good proof of concept.
I found the same problem, as far as I can tell the Arduino networking stack isn’t so powerful as to support DHCP. The bigger problem is that you can’t add proxy settings to allow external traffic.