Use the RSS feed that appears on the recent comments page. I use reader.google.com to read my RSS feeds. This will allow you to scroll back in bulk using just the scrollbar then read at leisure. It also shows comments as 'read' or 'unread' based on where you are up to.
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.