How to get a Windows Phone 7's useragent string?

I need to get a phone's user agent string, but I haven't found anything in the API that allows this. I've come across the following two blog posts describing the format of the user agent string:

http://blogs.msdn.com/b/iemobile/archive/2010/03/25/ladies-and-gentlemen-please-welcome-the-ie-mobile-user-agent-string.aspx

http://madskristensen.net/post/Windows-Phone-7-user-agents.aspx

But I haven't found a method that can return the user agent. Has anyone been able to do this successfully?