What are the chances that the plug could be powered with an internal lithium ion battery ans still look pretty good. While the whole point of the system is to be plugged in, I think that such a small board lends itself to a portable application. The 5 volt Dc could easily be supplied by an external battery back, but that is not so compact.
An internal battery would work but would require a charger system as well. http://www.sparkfun.com/commerce/product_info.php?products_id=726
Would the plug work off 3.7 volt? I wonder whether the 2.5 V pins could be used. A DC step up unit could be used.