Override Backbone toJSON

Salve galera,

Outro dia precisei sobreescrever o toJSON do Backbone Model.. fica ai a dica de como fazer

    // method override
    toJSON: function () {

        if (this.beforePost)
            this.beforePost();

        // call the "super" method 
        var json = Backbone.Model.prototype.toJSON.call(this);

        // here manipule the json objeto ;)

        return json;
    }

Eu precisava alterar o comportamento para que, quando fosse criado um objeto para o post, alguns atributos mudassem de nome no json, assim:

    // mapper properties to swap values
    properiesMap: [
        { from: 'TaskGroup', to: 'TaskGroupId' },
        { from: 'TaskType', to: 'TaskTypeId' },
        { from: 'UserProfile', to: 'UserProfileId' },
        { from: 'Sprint', to: 'SprintId' },
        { from: 'BacklogItem', to: 'BacklogItemId' },
        { from: 'Status', to: 'Status' },
    ],

    // call before json creation
    beforePost: function() {
        this.attributes['Content'] = $(".form-task").find("[name='Content']").val();
        this.attributes['BacklogItem'].Id = parseInt($("#backlogItemId").val());
    },

    // call to create json to post
    toPostJson: function () {

        if (this.beforePost)
            this.beforePost();

        // the original toJSON
        var json = Backbone.Model.prototype.toJSON.call(this);

        for (var i = 0; i < this.properiesMap.length; i++) {
            var it = this.properiesMap[i];
            json[it.to] = this.get(it.from).Id;

            if (it.from != it.to)
                delete json[it.from];
        }

        return json;
    }