Currently Being ModeratedJun 16, 2013 8:11 AM (in response to MLadd)
One setup that may work for you is to log in and authenticate on your portable, then share that connection either directly to the AppleTV (via Ethernet) or to your Airport Express (and create a wireless LAN). This setup will require that your portable stays on and awake, and may need to stay connected to power during this type of usage. Take a look at the article below for more information on Internet sharing.
Hope that helps,