Without ClearPass, the administrative burden is more on you to keep up with. In your case, you could add Mac Authentication to your visitor SSID. The Smart TV would be registered within the controller’s internal database so that connections from the TV are placed directly into the Visitor’s post-Auth role...bypassing the captive portal.
The downside to doing this without ClearPass is two fold. First, you have to maintain the database of authorized SmartTVs yourself, vs offloading device registration to the users. Second, there is no mitigation for Mac cloning. Anyone cloning their MAC address to a known working Smart TV will have access to the Visitor SSID without accessing the portal. However, it will allow your SmartTV to share the visitor network without getting stuck in the captive portal role.