I've prepared a small project that demonstrates how to achieve this functionality. Have a look at it and let me know how it works for you. Let me know if you encounter any further issues.
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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