WPF DataGrid AutoGenerated columns and CellStyle accessing DataTable value

using System;
using System.Data;
using System.Globalization;
using System.Windows.Controls;
using System.Windows.Data;

namespace PreQuant
{
  public class CellToolTipConverter : IMultiValueConverter
  {
    #region IMultiValueConverter Members
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
      if (values == null)
        throw new ArgumentNullException("values");
      if (values.Length != 2)
        throw new InvalidOperationException("Incorrect number of values passed to CellToolTipConverter");
      DataRowView rowView = values[0] as DataRowView;
      if (rowView == null)
        throw new InvalidOperationException("Incorrect type of first (DataRowView) value passed to CellToolTipConverter");
      DataRow row = rowView.Row;
      if (row == null)
        throw new InvalidOperationException("DataRow must not be null");
      DataGridCell cell = values[1] as DataGridCell;
      if (cell == null)
        throw new InvalidOperationException("Incorrect type of second (DataGridCell) value passed to CellToolTipConverter");
      DataGridColumn column = cell.Column;
      if (column == null)
        throw new InvalidOperationException("DataGridColumn must not be null");
      string toolTip = null;
      CellViewModel vm = row[column.SortMemberPath] as CellViewModel;
      // because I also had renamed the columns from the DataTable column names, I used .SortMemberPath
      // It had to repeat the logic of the RowStyle ToolTip generation since the CellStyle supercedes the RowStyle
      // ...
      // Then it could use the CellViewModel to get the cell's toolTip (if the row hasn't already set one...
      toolTip = vm.Information;
      return toolTip;
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
      throw new NotImplementedException();
    }
    #endregion
  }
}

<Style x:Key="CellStyle"
       TargetType="{x:Type DataGridCell}">
  <Setter Property="ToolTip">
    <Setter.Value>
      <MultiBinding Converter="{StaticResource CellToolTip}">
        <Binding />
        <Binding RelativeSource="{RelativeSource Self}" />
      </MultiBinding>
    </Setter.Value>
  </Setter>
</Style>

ToolTip="{Binding Path=Content.yourPropertyPath, RelativeSource={RelativeSource TemplatedParent}}"