.Read(read => read.Action("GetRecords", "SoftwareSecurity", new { showAll = false }))

public ActionResult GetRecords([DataSourceRequest] DataSourceRequest request, bool showAll = false)
    {
        int total = 0;
        string filter = Request.Form["filter"];
        string sort = Request.Form["sort"];
        int pageSize = Convert.ToInt32(Request.Form["pageSize"]);
        int pageNum = Convert.ToInt32(Request.Form["page"]);

        [rest of code not needed for here.....] (returns json)

}

function showAll() {
    var grid = $("#userAccessGrid").data("kendoGrid");
    $filter = new Array();
    $filter.push({ field: "CustID", operator: "gt", value: "0" });
    grid.dataSource.filter($filter);
}