Dynamic loading imports in Polymer circa 1/17/2014. Will be very much streamlined shortly.

gistfile1.js

      loadLinks: function(urls, callback) {
        var doc = document.createDocumentFragment();
        urls.forEach(function(url) {
          var link = doc.appendChild(document.createElement('link'));
          link.rel = "import";
          link.href = url;
        });
        // load-all-links in document method should be factored somewhere
        // very similar method used in x-meta
        HTMLImports.importer.load(doc, function() {
          doc.querySelectorAll('link').array().forEach(
            function(link) {
              HTMLImports.parser.parse(link.content);
              CustomElements.parser.parse(link.content);
            }
          );
          callback && callback();
        }.bind(this));
      }