Experimental Sitecore ControllerRunner with childaction behaviour. Based on the AreaControllerRunner from the Sitecore.MVC.Contrib project.

AreaControlllerRunner.cs

using Sitecore.Mvc.Controllers;
using System.Web.Mvc;
using System.Web.Routing;
using Sitecore.Mvc.Presentation;
using Sitecore.Mvc.Common;

namespace Sitecore.Mvc.Contrib.Controllers
{
    public class AreaControllerRunner : ControllerRunner, IControllerRunner
    {
        private readonly IPageContext _pageContext;

        public AreaControllerRunner(IPageContext pageContext, AreaRouteData areaRouteData)
            : base(areaRouteData.Controller, areaRouteData.Action)
        {
            _pageContext = pageContext;
            Area = areaRouteData.Area;
        }

        public AreaControllerRunner(AreaRouteData areaRouteData) 
            : this(new PageContextWrapper(PageContext.Current), areaRouteData)
        {
        }

        public string Area { get; set; }
        
        protected override void ExecuteController(Controller controller)
        {
            RequestContext requestContext = _pageContext.RequestContext;

            object controllerValue = requestContext.RouteData.Values["controller"];
            object actionValue = requestContext.RouteData.Values["action"];
            object areaValue = requestContext.RouteData.DataTokens["area"];
            object parentViewContextValue = requestContext.RouteData.DataTokens["ParentActionViewContext"];

            try
            {
                requestContext.RouteData.Values["controller"] = ActualControllerName;
                requestContext.RouteData.Values["action"] = ActionName;
                requestContext.RouteData.DataTokens["area"] = Area;
                requestContext.RouteData.DataTokens["ParentActionViewContext"] = GetHtmlHelper().ViewContext;
                // TODO: Investigate if routeValues will needs to be merged in. 
                // ChildActionValueProvider is used when you issue a child request using Html.Action and/or 
                // Html.RenderAction methods, so that your explicit parameter values in Html.Action and/or 
                // Html.RenderAction will always take precedence over other value providers.
                //if (dictionary != null)
                //{
                //    routeValues[ChildActionValueProvider.ChildActionValuesKey] = new DictionaryValueProvider<object>(dictionary, CultureInfo.InvariantCulture);
                //}

                ((IController)controller).Execute(_pageContext.RequestContext);
            }
            finally
            {
                requestContext.RouteData.Values["controller"] = controllerValue;
                requestContext.RouteData.Values["action"] = actionValue;
                requestContext.RouteData.DataTokens["area"] = areaValue;

                // TODO: Investigate if parentViewContextValue is always null. Test with nested ControllerRenderers.
                if (parentViewContextValue == null)
                    requestContext.RouteData.DataTokens.Remove("ParentActionViewContext");
                else
                    requestContext.RouteData.DataTokens["ParentActionViewContext"] = parentViewContextValue;
            }
        }

        protected virtual HtmlHelper GetHtmlHelper()
        {
            ViewContext current = ContextService.Get().GetCurrent<ViewContext>();
            return new HtmlHelper(current, new ViewDataContainer(current.ViewData));
        }
    }
}