Thank you for this! We tried googling a workaround, but got nowhere.What you want to do is unplug the network cable at the back first and power cycle the TV. The network cable sends programming instructions that disable the HDMI port. This has worked for us every time in the last thee years - including on the WBPC sailing in March on the Wonder (even if unusable because of the small screen). More on the approach:
https://lifehacker.com/how-to-outsmart-your-hotel-room-tv-and-use-its-hdmi-por-1841694937
You may also want to pick up a right angle HDMI adapter to work with the flush mounts:
https://www.amazon.com/VCE-Supported-Degree-Female-Adapter/dp/B00Y7UT6EK/
Although, it appears it may not work if the remote becomes disabled. The TV in the Grand Californian room did not have ANY external buttons at all. We looked on all edges, in the back, etc. Without the remote, the TV is unusable. We did unplug the main HDMI cable that was plugged into the box on the back, and then the remote wouldn't work at all. So, this trick may not work in all cases.