I like this idea. A quick/dirty way to sort of get there is to show a prominent "Share your post to help getting replies" on the thread_view page based on certain conditions. After posting, the user will be redirected to the thread view.
This conditional will show the more prominent share buttons only to the thread author while there are no replies:
<xf:if is="$thread.reply_count==0 and $xf.visitor.username==$thread.username">
Show Prominent Share Social Buttons
</xf:if>