I don't think you can. If my memory doesn't hate me, I think the best that can be done is if a Mod locks it and the thread slowly dies through the pages.
You can always use the report button and request your threads to be closed or removed by a moderator. And don't worry, you wouldn't be the first to do this. The report button is multi-functional, so whenever there something you need a moderator to handle, you are welcome to use it. So, I guess that means the question has been answered, so I'll close this thread now.