I read a lot of archived stories, and when I finish, often I'd like to be able to add a comment (saged of course, but you can't comment with archive), because really, there isn't any where else to comment about the story (other than a casual reference elsewhere). Maybe about the development, ending or lackof, or address the author. I'd think I'd even enjoy reading other people's comments slowly accumulated over the months/years. It kinda feels cold and empty when you finish a story that had you emotionally, intellectually or otherwise hooked, and everything froze the day the story finished. I know there are probably good reasons for the archive being unpostable, but still.
Just create a thread here or in /gensokyo/ to talk about finished stories. Sounds like the best solution. Bumping threads would just piss people off and I'm sure you're not the only one who feels like that. Some of the authors of those stories are still around and liable to see any discussion. Alternatively, you can try to talk about stories in IRC, though that may require good timing.