i can speak only for the Sharp Aquos LC320E (22 inch)
There's indeed no post with a good solution... and this is indeed sooo old... ;-)
So instead of wasting my time on forums etc, i just called up sharp and the very first person i spoke to was able to assist me, isn't that great? So here are the steps to make it working:
- turn of the tv
- hold the vol+ , vol- , input selection
- power on the tv while still holding the other buttons
- it will show you a log in password: 027
- now you should see a screen with many options, look for the "hotel..." and enable this. (i think i also enabled the one just above that with serial port... but perhaps not needed at all)
- power cycle the tv

You should now be able to power on the tv even when it's in sleep mode.

PS. in the Legrand concept store (tv's controlled by Vantage) we had also the bigger ones (27 inch) and they needed no change like the 22 inch ones...
So don't be angry if this method doesn't work for your type of tv, but you could give it a try huh?!
Good luck, Pascal