You could accomplish this yourself. Add an event listener to watch for the android back button pressed. Here is a code sample that should accomplish this. There are two event listeners because Android emits different events depending on the version. See docs.
$.drawer.window.addEventListener('android:back', androidBackPressed);
$.drawer.window.addEventListener('androidback', androidBackPressed);
function androidBackPressed() {
if ($.drawer.isLeftWindowOpen) {
$.drawer.toggleLeftWindow();
}