This thread is probably too long and people have lost interest, but I'll throw in my two cents anyway.
1. Who will actually be watching Coventry vs Sheffield on Sky? Barely anyone. So, what statement will an empty ground make? You need to give people something to look at. There are so many empty grounds in the lower leagues. The positioning of cameras can also make a relatively full stadium look dead. It being empty wont really matter. It can very easily be mistaken for apathy.
2. Getting a report about people on the hill on Sky Sports News and Midlands Today will not sway many people. It'll be the same old protest and it'll be boring, sorry to say.
So, how do we get around this?
The merits of the mass walk out is that Sky will notice that the attendance, which is usually circa 2000, is suddenly bolstered. They'll make a comment on it and say something like "A surprising turn out by Coventry City fans who have been boycotting these games". Make them notice us, as we've been conspicuous in our absense. Then walk out. They've acknowledged we're there and they can't ignore the fact we've left very early. If we leave in an entertaining way, this will capture people's attention. It'll get video clips, it can stand a chance of going viral if we get the video to the right people. Maybe even film it ourselves from several angles.
If you're intent on NOPM and staying on that hill, then you have to give people something to talk about. Banners and stuff wont go far, fireworks, flares etc will. Be loud, intrusive and make sure you can't be ignored. If no one is pointing cameras at you, then point them at yourselves and get those videos out there.
The Guardian does video blogs about sports, Soccer AM will probably have it, get it on youtube and share it far and wide: "Look what these fans are doing."