RadGridView has no built-in support for pivoting the data source. Having this in mind I do not recommend changing the default templates to try to simulate pivoting simply because you will end up with a lot of modified and ugly XAML and most probably many features will not work as expected.
Another option is to pivot the data itself as demonstrates here. Unfortunately this approach might not be applicable to your scenario. Could you please try it and let me know if it works as expected.
the Telerik team
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