What about asking new users how much of the article they read?
So before commenting you need to fill in how much of the article you actually read, with predefined options: 0/20/40/60/80/100%. This will then be shown in the comment. Of course people can lie but I think:
- It is hard to lie for most people or at least a bit uncomfortable.
- If someone filled in
100%but obviously did not read the article I think it’s easier to give some kind of warning.