Adding a SortExpression property to the columns including template and bound column types would enable users to sort on template columns and override the default sort for bound columns.
Closing the thread per Alex's comment
Is this a duplicate of this idea: http://kendoui-feedback.telerik.com/forums/127393-telerik-kendo-ui-feedback/suggestions/3026892-ability-to-do-custom-sort-on-the-grid