Just playing the Devil's Advocate here, but couldn't you consider user training of an application using SQL Server 2005 as the database backend a "demonstration use"?
You can have SQL Server 2005 Developer Edition loaded on development, QA, UAT servers (not desktop systems) with each developer the develops and modifies code on these servers with a licensed copy of Developer Edition. You can then have QA and Users (not licensed) testing against these same servers without violating the licenses for SQL Server 2005 Developer Edition AS LONG AS those individuals are not creating/modifying code on the server.
Based on that, why couldn't you also train users against that some environment? It isn't production.
Final note, contact Microsoft and ask them directly. I know that the Development/QA/UAT is valid as that question has been asked many times on this site and several people who asked later reported back that is was true after contacting Microsoft.