From http://webapps.stackexchange.com/a/18885 and http://pebblecodeblog.disqus.com/admin/tumblr/, I found that you can show disqus comments with
<a class="dsq-comment-count" href="{Permalink}#disqus_thread">Comments</a>
which seems to generate "x Comments" where x is the number of comments. Is there a way to get rid of the "Comments" bit, and just have the number?