如何创建带有一些初始化字段（Id除外）的NHibernate代理对象？

public class User
{
    protected User() {

    }

    public User(int id, string username, string email) {
        // ... 
    }

    // initialize the following fields from other datasources
    public virtual int Id { get; set; }
    public virtual string UserName { get; set; }
    public virtual string Email { get; set; }

    // the rest of fields when accessed will trigger a select by id in the database
    public virtual string Field1 { get; set; }
    public virtual string Field2 { get; set; }
    public virtual DateTime Field3 { get; set; }
    public virtual ISet<Comment> Comments { get; set; }
}

        // create User object proxy with some fields initialized
        var user = Session.Load<User>(5, new { UserName = \"admin\", Email = \"admin@company.com\" });
        Console.WriteLine(user.Id); // doesn\'t hit the database
        Console.WriteLine(user.UserName); // doesn\'t hit the database
        Console.WriteLine(user.FullName); // doesn\'t hit the database
        if (somecondition) {
            Console.WriteLine(user.Field1); // fetches all other fields 
        }