You can do this in QueryNextCurrentCellPosition.
private void gridControl1_QueryNextCurrentCellPosition(object sender, GridQueryNextCurrentCellPositionEventArgs e)
{
if(e.ColIndex > this.gridControl1.ColCount)
{
this.gridControl1.CurrentCell.EndEdit();
if(this.gridControl1.CurrentCell.Renderer.Control != null
&& this.gridControl1.CurrentCell.Renderer.Control.Visible)
{
this.gridControl1.CurrentCell.Renderer.Control.Hide();
}
e.Handled = true;
e.Result = false;
}
}