如何在外部Enterprise Library配置文件中指定实体框架代码第一个连接字符串

I am creating a WPF application, having classical architecture: UI layer, business logic layer and infrastructure layer. I decided to split configuration in two files: app.config file, containing common app configuration, and dll.config, containing connection string to use in DbContext for domain model storage. The second .config file should be sticked to business logic DLL, while first file sticked to corresponding UI executable (there will be one more UI with it's own configuration).I am creating a WPF application, having classic