How to configure a custom SiteMapNode for a sitemap

A rather dull question, so no surprise it didn't get a response! For anyone else who may stumble across this problem, here's my preferred solution:

I've found the best way to handle this is to load the physical site map into an xml document. I then have a NavigationNodeFactory, which validates and builds my own composite NavigationNode tree from the xml document.

My NavigationNode class is as opinionated as I like and circumnavigates the issues I found with SiteMap and SiteMapProvider, namely poor testability for implementers.

Apparently it's not possible due to optimizations by Microsoft. The base class to be used instead is StaticSiteMapProvider.