Hey there,
the only solution I can come up with right now is to drag in a HTML embed box and write some code to make a custom button. I just tested with this and it seems to be working fine;
<div class="button" onclick="Calendly.showPopupWidget('YOUR_SCHEDULING_LINK');return false;"
style="width: 200px; background: #ebebeb; color: #333; padding: 20px; text-align: center; border-radius: 100px;
">Calendly</div>
It’s just a simple light grey button with the text “Calendly”. 