Quick note... this may actually be rather annoying as it shifts the editor out of where the user is initially editing. But this should do it...
Template: quick_reply_macros
Find:
Code:
<xf:if is="$showPreviewButton">
<div class="js-previewContainer"></div>
</xf:if>
Move right below:
Code:
<div class="message-cell message-cell--main">{/code]