I had to do something similar at a client site, but it required a PC and the TV became a large monitor. If you are trying to access CRM via the out of the box CRM web site, compatibility with the TV's built in browser could be an issue. CRM does
support most modern browsers, but TV's are another story.
As far as I am aware, there are no plugins or coding magic out of the box to do this, sorry. :)
Your idea of a Portal is probably the best. Setup a separate web site application that accesses the CRM web services and displays the data you want to show on the TV screens, and then just make sure that the TV's built in browser can display it properly.
Keep the site as simple as possible without a lot of fancy JS to ensure compatibility.
Good luck!