Add this file to your umbraco 4.7 App_Code and you will be able to add json-returning functions to base-urls

BaseAsJson.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using umbraco.presentation.umbracobase;
using System.Web.Script.Serialization;

namespace BaseAsJson
{

    /// <summary>
    /// 
    ///  Add this file to your umbraco 4.7 App_Code and you will be able to add json-returning functions to base-urls directly in your razor macros
    /// 
    /// 
    ///  Example 1. Set url-aware session variable value (for the current usersession)
    ///  
    ///       Add this code in a razor-script:
    ///  
    ///       Session["/base/asjson/session/value/"] = "can I haz";
    ///       
    ///       Then you can use that url (/base/asjson/session/value/) to get that value ("can I haz")
    ///       
    ///       you can use this for dynamic values or complex objects aswell, like an array of values, for example for some auto-complete
    ///       
    ///       Session["/base/asjson/session/array/"] = new[] {"one", "two", "three"};
    ///
    /// 
    ///  Example 2. Set url-aware session function (for the current usersession)
    ///  
    ///       Add this code in a razor-script:
    ///  
    ///       Session["/base/asjson/session/func1/"] = new Func<object>(()=>
    ///       {     
    ///          return new { xxx="some string", currentdate=DateTime.Now.ToShortDateString()};
    ///       });
    ///       
    ///       Then you can use that url (/base/asjson/session/func1/) to get that json { xxx:"some string", currentdate:"2012-04-02" }
    ///       
    /// 
    ///  Example 3. Set url-aware session function with parameter (for the current usersession)
    ///  
    ///       Add this code in a razor-script:
    ///  
    ///       Session["/base/asjson/session/getnode/"] = new Func<string, object>((param)=>
    ///       {     
    ///         var node = new umbraco.NodeFactory.Node(Convert.ToInt32(param));
    ///         return new {name = node.Name};
    ///       });
    ///       
    ///       Then you can use that url (/base/asjson/session/getnode/1065) to get that json { name:"Home Page" }
    /// 
    /// 
    ///  Example 4. Set url-aware application variable value (for any user)
    ///  
    ///       There are also a possiblity to add the functionality to the App object to make it useable outside of session context. (Works with all examples 1,2,3, just change session to app)
    ///       
    ///       Add this code as a razor-macro in the master template - or any page that is likely to get requested - for the App value to be initialized:
    ///  
    ///       if ("App["/base/asjson/app/value/"]==null) { App["/base/asjson/app/value/"] = "can I haz"; }
    ///       
    ///       Then you can use that url (/base/asjson/app/value/) to get that value
    /// 

    /// 
    /// 
    /// </summary>

    [RestExtension("asjson")]
    public class asjson
    {
        private static void writeObject(object obj, string parameter = "")
        {
            object result;

            if (obj != null)
            {
                if (obj is Func<string, object>)
                    result = ((Func<string, object>)obj).Invoke(parameter);
                else if (obj is Func<object>)
                    result = ((Func<object>)obj).Invoke();
                else
                    result = obj;
            }
            else
                result = null;

            HttpContext.Current.Response.ContentType = "application/json";

            var js = new JavaScriptSerializer();
            HttpContext.Current.Response.Write(js.Serialize(result));
        }

        [RestExtensionMethod(returnXml = false)]
        public static void app(string target, string parameter)
        {
            target = "/base/asjson/app/" + target + "/";
            writeObject(HttpContext.Current.Application[target], parameter);
        }
        [RestExtensionMethod(returnXml = false)]
        public static void session(string target, string parameter)
        {
            target = "/base/asjson/session/" + target + "/";
            writeObject(HttpContext.Current.Session[target], parameter);
        }
    }
}