scriptmanager.cs

public static void class ScriptManagerExtensions {
  public static RegisterJsonObject(this ScriptManager manager, Page page, Object obj, string varName) {
    var serialized = SERIALIZE(obj); //make this use your JSON library
    var createVar = "; " + varName + " = " + serialized + ";";
    manager.RegisterClientScriptBlock(page, page.GetType(), varName, createVar, true);
  }
}