I've already mentioned sticking white A4 sheets with gone written on them to the empty seats (even got the like off Nick) couple this with something like a silent protest during the game or a sit in after the game will probably get more attention.
A silent protest will probably be easier as we're best part there anyway and with the on the pitch performances it's hard enough to get people to stay to the end as it is let alone hang around for 30 minutes after a game.
And just keep doing this at home games until someone starts listening.