I could have sworn we have a CSS class on the post that indicates “this is the topic creator” for subsequent posts in the topic, I checked the HTML via f12 and ah yes there it is:
<div class="topic-post clearfix topic-owner regular">
<article id="post_3" data-post-id="177932" data-user-id="17648" class="boxed onscreen-post" style="">
Target the <div> with the class of topic-owner and you can make those posts stand out.