I don't think there is anything that can be done which hasn't already been done in the last 15 years, which isn't illegal.
Fans have involved MPs, spoken to regional, national, international press, supporter federations, protested inside the ground, outside the ground, brought livestock into the ground, done planned walkouts, thrown a snowball, chanted endlessly, made banners and at least two thirds of the fan base have just stopped attending. No one outside of East Lancashire cares about the issue. I'm not aware of anything else that people can do.
Emptying the stadium is the one final thing which hasn't been done.