I'm not sure why you think Captcha or similar won't help/stop the attacks. Unless someone has come up with a way for the images to be properly recognized, that is.

1) Force EVERY EXISTING USER to do a Captcha ONCE on the next login, then allow them to login and post as usual from that point forward. Give users a message as to why this action is being required once.

2) Force every NEWLY CREATED USER to do a Captcha before said user is actually created.

Would this not be workable?

As it is, SSC.com is being relegated to non-functionality and it won't take long for users to abandon it in droves (if that hasn't already happened).