A knockout datepicker data binder can be found here: jQuery UI datepicker change event not caught by KnockoutJS
In order to hide the dates (which is the only thing that triggers datepicker's output), I do this for the sans knockout solution:
$(".monthPicker").focus(function () {
    $(".ui-datepicker-calendar").hide();
});
$(".monthPicker").datepicker({
    dateFormat: 'MM yy,
    changeMonth: true,
    changeYear: true,
    showButtonPanel: true,
    onClose: function(dateText, inst) {
        var month = $("#ui-datepicker-div .ui-datepicker-month :selected").val();
        var year = $("#ui-datepicker-div .ui-datepicker-year :selected").val();
        $(this).val($.datepicker.formatDate('MM yy', new Date(year, month, 1)));
    }
});
This works.
But how do I get this working with knockout's data binder?
 
    