I took the approach of adding an 'overview' page as the first item in the folder.
Then I added the following code into the Code Injection section of the advanced settings, to make clicks on that folder go to its first subpage instead.
<script>
var folders = document.querySelectorAll('.folder-collection > a'),
folder_click = function () {
var a = this.parentNode.querySelector('.subnav a');
window.location = a.href;
};
Array.prototype.forEach.call(folders, function (folder) {
folder.addEventListener('click', folder_click);
});
</script>
Also: the fol