How to disable sorting for few rows in asp.net gridview

Question

Hi i'm showing some data in gridview which is sortable. I want to disable sorting for few rows based when date is not null.

below is the code

  griddata.datasource = dt;
    griddata.databind();
    if(condtion...)
     griddata.Rows[2].Enabled = false;
     griddata.Rows[3].Enabled = false;

but this is not working.With this code i can still able to sort.Please help me out.