<script type="text/x-handlebars" data-template-name="components/latest-topic-list-item">
<div class="topic-poster" data-user-card="{{topic.creator.username}}">
Maybe try adding the username/userid property to the topic poster div by override latest-topic-list-item template then you can hide them through user stylesheet.
I also have a component to auto-hide ignored user if you would like to take a look.