Retroactive Spam Solutions!

Okay, I’d like to get this settled once and for all. Been searching this for hours to no avail.

Before I started using AKismet, my blog was flooded with spam. Now, I don’t get any more spam on the newer posts, but the old posts have literally thousands and thousands of spam comments.

How do I get rid of them?!

I can’t use Defensio on this version of WP. Disabling comments on those pages just disallows new comments but doesn’t hide the old ones.

They don’t necessarily have to be deleted, hidden would be fine. I don’t mind editing details on particular pages or editing php (perhaps to check below a certain ID value), but I’m not going through and deleting 20,000 spam comments manually.

Surely somebody has solved this before, what is the best solution?

Thanks ever so much,
Rich