No, but I think something like that could work in LJ, especially for a longer fic in several installments. Before chapter 1 there would be a sort of intro post: I've been working on a new fic, and some bad stuff happens in it. If you'd like more detailed warnings, please click here. If you'd prefer to be surprised, chapter 1 will be coming soon. And then in the heading of each of the following chapters there could be a link: More detailed warnings here.

I don't know though. It doesn't seem like a lot of effort to me, but some people want their warnings in flashing lights. Hmmm.