Access Server Side paramters on callback

moden

I have added an extra server side parameter:

ajax: {
            type: "POST",
            url: $("#ChildrenDatatableInitAddress").val(),
            datatype: "json",
            contentType: "application/json; charset=utf-8",
            headers: {
                "__RequestVerificationToken": $('input[name=__RequestVerificationToken]').val(),
            },
            data: 
                function (data) {
                data.sEcho = "echoChildren";
                data.draw = "drawChildren";
                data.GreaterThanFifty = "N";

                data.__RequestVerificationToken = $('input[name=__RequestVerificationToken]').val();

                return data = JSON.stringify(data)
            }
        },

The parameter is updated on the server and returned. How do I access the server parameter data.GreaterThanFifty on callback?

 "drawCallback": function (data)
        {
           ???????
        }