There are already several large threads in the travel technology forum about hacking hotel TVs. In Marriotts, the easiest thing to do is unplug the little RJ-45 (or the ilk) connecting the parasitic black box to the back of the TV. You lose the ability to use the remote control, but you gain the function of the hard buttons on the TV itself, and hence can change input sources. If the room has the desk with the multifunction patch panel, you can use VGA (D-sub) or HDMI to connect without doing any monkey business.