I have syndicated a lot of WordPress blogs and are now showing them on another site. However, I would like the reader to contribute with comments (through the other site). How can I post a comment for a blog post without using the WordPress form?
Add WordPress comment from an external site
It sounds like you are using standard WordPress commenting system? You could move your comments to Disqus by using the Disqus Comment System Plugin available for WordPress, then just setup your sites to all run off of the same account?