JSON mixin like underscore extend for dotNet (works on JSON strings not Objects). Relies on Newtonsoft.Json from http://json.net

JSON.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using Newtonsoft.Json;

namespace CopenhagenCode
{
    public class JSON
    {
        public static string Mixin(string json1, string json2)
        {
            StringBuilder sb = new StringBuilder();
            StringWriter sw = new StringWriter(sb);
            var writtenValues = new Dictionary<string,bool>();
            using (JsonWriter writer = new JsonTextWriter(sw))
            {
                writer.Formatting = Formatting.None;

                writer.WriteStartObject();
                writeJson(writer, json2, writtenValues);
                writeJson(writer, json1, writtenValues);
                writer.WriteEndObject();
            }
            return sb.ToString();
        }

        static private void writeJson(JsonWriter writer, string json, Dictionary<string, bool> writtenValues)
        {
            JsonTextReader reader = new JsonTextReader(new StringReader(json));
            var objectDepth = 0;
            var writeProperty = true;
            while (reader.Read())
            {

                switch (reader.TokenType)
                {
                    case JsonToken.PropertyName:
                        if (objectDepth == 1)
                        {
                            var propertyName = (string)reader.Value;
                            if (writtenValues.ContainsKey(propertyName))
                            {
                                writeProperty = false; //do not write properties on depth 0 that are already written
                            }
                            else
                            {
                                writtenValues[propertyName] = true;
                                writeProperty = true;
                            }
                        }
                        if (writeProperty)
                        {
                            writer.WriteToken(reader);
                        }
                        break;
                    case JsonToken.EndObject:
                        objectDepth--;
                        if (objectDepth == 0)
                        {
                            return;
                        }
                        if (writeProperty)
                        {
                            writer.WriteEndObject();
                        }
                        break;
                    case JsonToken.StartObject:
                        if (objectDepth != 0 && writeProperty)
                        {
                            writer.WriteStartObject();
                        }
                        objectDepth++;
                        break;
                    default:
                        if (writeProperty)
                        {
                            writer.WriteToken(reader);
                        }
                        break;
                }
            }
        }
    }
}

I am thinking of using JSON.NET for REST calls. However, I really like the mixins of Jackson that use annotations to build class objects from the JSON payload. Can I use this class for that or does it have another way of doing things? Perhaps could you write a simple client class to show how this mixin is used.

It works like underscores .extend method, except it works on JSON strings and outputs a JSON string. Does not build any objects, just strings.