Need Comment Editing Plugin

Askimet is missing a TON of spam, lately, and I’m having to spend a significant amount of time, each day, manually marking comments as spam. Unfortunately, I’m having to do this manually on each comment. Is there any way to mass-edit already approved comments, and mark them spam? Currently, WP seems to only support mass-deletion… perhaps there is a plugin?

Also, is there anything I can do to enhance Askimet’s ability to stop the spam in question?