Plugin - Admin Popup, Return to Widget/widgetId

I'm designing a new plugin using the Widget interface but am having difficulty with one particular part.  It's probably a newbie problem to have but for some reason I just can't get it fixed.  So far everything else is working great on the plugin except this.  Once it's finished I will likely be contributing it to the community.

In the widget config view, I have a popup screen which allows users to select topics from a list model.

On form submit, topics are saved and linked to the proper widget entity but I can't figure out what return value to use in the controller.  Since 'Configure' in my plugin controller is a Child Action, I can't return directly to that (or at least I don't know how to).  I think I need to return to the Widget controller, Edit Action for the proper widgetId, I just can't seem to figure out the syntax.  

Below is the code for TopicAddPopup in my plugin controller.  I've also got a btnId and formId which I believe is being passed from the button which brings up the popup.  At some point I added these thinking it would help in my solution.  I guess I'm just a bit lost on this one.

        [HttpPost]
        [FormValueRequired("save")]
        public ActionResult TopicAddPopup(string btnId, string formId, TopicBannerModel.AddBannerTopicsModel model)
        {
            if (model.SelectedTopicIds != null)
            {
                foreach (int id in model.SelectedTopicIds)
                {
                    var topic = _topicService.GetTopicById(id);
                    if (topic != null)
                    {
                        _tbService.InsertBannerTopic(
                            new BannerTopicsRecord()
                            {
                                WidgetId = model.WidgetId,
                                TopicId = id,
                                DisplayOrder = 1
                            });
                    }
                }
            }
            ViewBag.RefreshPage = true;
            ViewBag.btnId = btnId;
            ViewBag.formId = formId;
            model.BannerTopics = new GridModel<TopicModel>();
            return null;
            //return View("~/Administration/Views/Widget/Edit.cshtml", model.WidgetId);
        }

Thanks in advance for any help.

Actually, nevermind.  I was able to bug check and complete the project.  Found a decent solution for the return on the popup.  Basically just needed to use the same return on the HTTP Post as the original popup action.