如何在Entity Frameworks 4.0 Model中指定SQL Server XML数据类型？

I'm building an ORM using Entity Frameworks 4.0 (CTP5) in the Model-First pattern. A few of my entities have complex (object tree) properties that don't need to be ORM entities - they're only of interest to back-end server systems that use this database, not to the clients that use this database. I'm building an ORM using Entity Frameworks 4.0