I suggest to visually distinguish the username of the post's creator within the discussions below their post.

Personally, this would save me from having to go to the top of the page often to (re)read the poster's username -- and losing my progress in the discussion in the process.

Also, I think such feature would be especially valuable in Ask HN and Show HN posts, where interactions from the Ask-er or Show-er can be integral to the discussion.

A simple way to do this with minimal visual noise would be to bold their username whenever they comment in the discussion.

Perhaps a limited test run in just these types of posts could be a good starting point.