Thanks. My game already relies heavily on AJAX and PHP so I could techically code another script to handle the comments.
The thing is, there are great tools out there (like the aforementioned Facebook or Disqus) which have things like user accounts and security covered, so I would basically be reinventing the wheel.
I was hoping for some hacky (or not) way to bring these tools to my game. Apparently there isn't an easy way out of this so I'll have a look at the possibility of wrapping these things in a plugin and if that proves too cumbersome I'll do as you suggest... code it anew. Meh.