It is not possible to force the RadMenu to call LoadContentFile without code-behind, but there are many ways, depending on your scenario, to execute code behind in Sharepoint. You should do a search on "Sharepoint code behind" or something similar and research the possible approaches. You can start with the article at http://msdn.microsoft.com/en-us/library/bb986729.aspx
as it explains how to add code-behind files to master pages.
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