I saw that some 2channelers was making a petition 署名活動 and there is supposed to be demos today (and next sunday . more precisely : http://www25.atwiki.jp/2ch-syomei/ )... I don't see what else we could do....
By the way, some people say that 2ch will not close because hiroyuki is not the owner of the domain or something like that, I don't know if it's true....
結論として署名活動かデモかそれぐらいしかないかな････