Make FilteringSelect closable on blur only

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/dojo/1.9.0/dijit/themes/claro/claro.css">
<select id="deptSelector"></select>
<div id="output"></div>

JavaScript

require(['dojo/_base/declare', 'dijit/form/FilteringSelect',
    'dijit/popup',
    'dijit/registry',
    'dojo/html',
    'dojo/store/Memory',
    'dojo/domReady!'], function (declare, FilteringSelect, popup, registry, html, Memory) {
        var CustomFilteringSelect = declare([FilteringSelect], {
            closeDropDown : function(/* Boolean */ focus){
                console.log("Not closing");
            },
            postCreate : function(){
                this.inherited(arguments);
                
            }
        });
        
    var departments = new Memory({
        data: [{
            id : 1,
            name: "Childcare Department",
            email: "[email protected]"
        }, {
            id : 2,
            name: "Health Goods Department",
            email: "[email protected]"
        }, {
            id : 3,
            name: "Medicine Department",
            email: "[email protected]"
        }, {
            id : 4,
            name: "Customer Service",
            email: "[email protected]"
        }, {
            id : 5,
            name: "Other Department",
            email: "[email protected]"
        },
        {
            id : 2,
            name: "Health Goods Department",
            email: "[email protected]"
        }, {
            id : 3,
            name: "Medicine Department",
            email: "[email protected]"
        }, {
            id : 4,
            name: "Customer Service",
            email: "[email protected]"
        }, {
            id : 5,
            name: "Other Department",
            email: "[email protected]"
        },
        {
            id : 2,
            name: "Health Goods Department",
            email: "[email protected]"
        }, {
            id : 3,
            name: "Medicine Department",
            email: "[email protected]"
        }, {
            id : 4,
            name: "Customer Service",
            email: "[email protected]"
        }, {
 ...