Silverlight 5, SharePoint 2010 and Require elevated trust when running in-browser

I cannot get a Silverlight 5 application hosted in the SharePoint SilverlightWebPart to have elevated trust.

Steps I have taken.

1. Edited the registry to allow the Silverlight 5 app to run elevated as per http://msdn.microsoft.com/en-us/library/gg192793%28v=vs.95%29.aspx

2. Signed the Silverlight 5 app and followed the steps in http://www.mistergoodcat.com/post/Silverlight-5-Tidbits-Trusted-applications

The Silverlight 5 app runs fine in Visual Studio 2012, but when I upload the xap file to SharePoint and try the same action,Application.Current.HasElevatedPermissions is always false (i.e. the Silverlight 5 app has not gone into elevated trust).

What additional steps have to be taken in SharePoint 2010 to make the SilverlightWebPart allow its enclosed XAP to go into elevated trust?

Dave Anderson