You could hide it by checking to see the url of the current page. If it matches the url for a pinned post, then don’t render the comments box. For instance, if you had an “About” page at /about and an “Archive” page at /archive, and those pages were pinned, you can do something like this:
// src: https://cdn.commento.io/js/commento.js
var topP = document.createElement("p");
topP.innerHTML = '<div id="commento"></div>';
var cont = document.getElementById("wrapper");
cont = document.getElementById("post-body");
var currentURL = window.location.href;
var isAboutPage = /\/about$/i.test(currentURL);
var isArchivePage = /\/archive$/i.test(currentURL);
if (cont !== null && !isAboutPage && !isArchivePage) {
cont.appendChild(topP);
}