Dependant combos on grid

Is possible to have dependant combos on a grid that are bound server side?

What I want to happen is somehow rebind the DataSource when another combo box in the grid changes.

So for example Combo A was Continents and Combo B was counties I would want to filter the country list (Combo B) depending on what is selected in the continents (Combo A).  I can’t see any server events that fire upon selecting a combo within a grid.

Note that to further complicate things my columns are dynamically created.  

Any help would be much appreciated!!!
 

Below is a shortened extract of my code:-

protected void uxResults_ItemDataBound(object sender, GridItemEventArgs e)

{

  GridDropDownListColumnEditor

combo = null;

  editMan = editedItem.EditManager;

  GridDataItem item = (GridDataItem)e.Item;

  if (e.Item is GridEditableItem )

  {

    if ((e.Item as GridEditableItem).IsInEditMode)

    {

      combo = editMan.GetColumnEditor(dr["Column Name"].ToString()) as GridDropDownListColumnEditor;

      combo.DataSource = ApplyFilter(item, combo, dr, ds);

      combo.DataBind();

    }

  }

}

"UserID is neither a DataColumn nor a DataRelation for table DefaultView"

1. How do you add a client side event handler to the GridCheckBoxColumn
2. How do you access the edit controls of the GridBoundColumns in that event handler.

Thanks,
Steve