hijacking toJSON for a Kendo UI MVVM model

json.js

$(function(){

  var ds = new kendo.data.DataSource({
    transport: {
      create: {
        url: "/api/registration.php",
        dataType: "json",
        type: "POST"
      },
      parameterMap: function(options, operation){
        var json = kendo.stringify(options)
        console.log("JSON to the server:", json);
        return json;
      }
    },
    autoSync: false,
    schema: {
      model: {
        id: "RegistrationID"
      }
    }
  });

  var viewModel = kendo.observable({
    firstName: "John",
    lastName: "Doe",
    genders: ["Male", "Female"],
    gender: "Male",
    agreed: false,
    confirmed: false,

    register: function(e) {
      e.preventDefault();

      ds.sync();
      this.set("confirmed", true);
    },

    startOver: function() {
      this.set("confirmed", false);
      this.set("agreed", false);
      this.set("gender", "Male");
      this.set("firstName", "John");
      this.set("lastName", "Doe");
    },

    toJSON: function(){
      return {
        a: "B",
        c: "d",
        foo: "BAR"
      }
    }
  });

  ds.add(viewModel);

  kendo.bind($("form"), viewModel);

});