Kendo UI Grid conditionally prevent editing

HTML

<link rel="stylesheet" href="http://cdn.kendostatic.com/2014.1.318/styles/kendo.common.min.css">
<link rel="stylesheet" href="http://cdn.kendostatic.com/2014.1.318/styles/kendo.default.min.css">
<script src="http://cdn.kendostatic.com/2014.1.318/js/jquery.min.js"></script>
<script src="http://cdn.kendostatic.com/2014.1.318/js/kendo.all.min.js"></script>
<div>Chai cannot be renamed</div>
<div id='grid'></div>

JavaScript

var products = [{
    ProductID: 1,
    ProductName: "Chai",
    SupplierID: 1,
    CategoryID: 1,
    QuantityPerUnit: "10 boxes x 20 bags",
    UnitPrice: 18.0000,
    UnitsInStock: 39,
    UnitsOnOrder: 0,
    ReorderLevel: 10,
    Discontinued: false,
    Category: {
        CategoryID: 1,
        CategoryName: "Beverages",
        Description: "Soft drinks, coffees, teas, beers, and ales"
    }
}, {
    ProductID: 2,
    ProductName: "Chang",
    SupplierID: 1,
    CategoryID: 1,
    QuantityPerUnit: "24 - 12 oz bottles",
    UnitPrice: 19.0000,
    UnitsInStock: 17,
    UnitsOnOrder: 40,
    ReorderLevel: 25,
    Discontinued: false,
    Category: {
        CategoryID: 1,
        CategoryName: "Beverages",
        Description: "Soft drinks, coffees, teas, beers, and ales"
    }
}, {
    ProductID: 3,
    ProductName: "Aniseed Syrup",
    SupplierID: 1,
    CategoryID: 2,
    QuantityPerUnit: "12 - 550 ml bottles",
    UnitPrice: 10.0000,
    UnitsInStock: 13,
    UnitsOnOrder: 70,
    ReorderLevel: 25,
    Discontinued: false,
    Category: {
        CategoryID: 2,
        CategoryName: "Condiments",
        Description: "Sweet and savory sauces, relishes, spreads, and seasonings"
    }
}];

var dataSource = new kendo.data.DataSource({
    pageSize: 20,
    data: products,
    autoSync: true,
    schema: {
        model: {
            id: "ProductID",
            fields: {
                ProductID: {
                    editable: false,
                    nullable: true
                },
                ProductName: {
                    validation: {
                        required: true
                    }
                },
                Category: {
                    defaultValue: {
                        CategoryID: 1,
                        CategoryName: "Beverages"
                    }
                },
                UnitPrice: {
                    type: "number",
                    validation: {
                        required:...