I am afraid that the only available way is by using the Device Designer and pick a "Desktop" device. Then you are free to organize your dashboard objects in the new layout (the 1920x1080 is the exact dimensions for big screens and TVs).
You may need also to duplicate some of your worksheets/charts because on a big TV you will need larger fonts (I would never go bellow 24pt) so you can reach people that are not close to the screen.
We all hope that Tableau can come with better ways to respond to responsive design but at the current version this is the way to go. It will take a bit of work but once is done you will feel great.
I hope this helps