I am not sure if I understand your scenario correctly. However, I prepared a sample project illustrating how to create a hierarchical TileView and populate it using LINQ to SQL.
Please take a look at it and let me know if this is what you had in mind or if you need more info.
On a side note, I'd like to inform you that we've just released an online tool that allows you to reduce the size of your Silverilght applications. For more information, please visit http://blogs.telerik.com/blogs/posts/10-06-10/telerik_assembly_minifier.aspx
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