Restrict Comments Per User Per Post

I’m moderating a blog that has become kind of popular, but a handful of people are dominating the comments. In some cases, we get over 60 or 70 comments from just 3 or 4 people, and they often post dozens of comments in the first hour or so after an entry is posted. This makes it really hard for other people to chime in and get their voices heard.

I can’t find any plugins that allow limiting comments to a certain number per post (per user) or, better still, enforce a delay between comments from a given commenter. Does anyone have any ideas or advice?