How do you create custom column heading when you do grouping in silverlight?

I have a datagrid which is grouped on a column. It does gr开发者_如何学Goouping properly but it shows column name + column value. But I want to show only the column value but not the column name. I remember reading there is a method I can overwrite which will allow me to create custom column headers. Could someone point me to the link? Thanks,

Now I use thrid party control, it has group header formatter.