It is possible.
We're using the videoroom plugin to do such thing.
But it's not out-of-the-box.
You need to create room by yourself.
For example by modyfing janus.attach() in videoroomtest.js:
               success: function () {
                   // Attach to video room test plugin
                   janus.attach(
                           {
                               plugin: "janus.plugin.videoroom",
                               success: function (pluginHandle) {
                                   $('#details').remove();
                                   sfutest = pluginHandle;
                                   Janus.log("Plugin attached! (" + sfutest.getPlugin() + ", id=" + sfutest.getId() + ")");
                                   Janus.log(" -- This is a publisher/manager");
                                   // Prepare the username registration
                                   $('#videojoin').removeClass('hide').show();
                                   $('#registernow').removeClass('hide').show();
                                   $('#register').click(registerUsername);
                                   $('#username').focus();
                                   $('#start').removeAttr('disabled').html("Stop")
                                           .click(function () {
                                               $(this).attr('disabled', true);
                                               janus.destroy();
                                           });
                                   var createRoom = {
                                       "request": "create",
                                       "record": true,
                                       "publishers": 2,
                                       "room": room,
                                       "bitrate": bandwidth,
                                   };
                                   sfutest.send({"message": createRoom});
                                   setTimeout(function(){
                                       autoRegister();
                                   }, 500);
                               },
helper methods:
function autoRegister() {
   username = getURLParameter("username");
   var register = { "request": "join", "room": room, "ptype": "publisher", "display": username };
   myusername = username;
   sfutest.send({"message": register});
}
function getURLParameter(name) {
       return decodeURI(
           (RegExp(name + '=' + '(.+?)(&|$)').exec(location.search)||[,null])[1]
       );