.. ance<T>() where T : Foo, new() {

The WCF Configuration Editor in the right-click menu on WCF Service Host app.config files.  You can, however, wire it up given a quick trick.  From the Tools menu choose WCF SvcConfigEditor and immediately close the editor.  Until you close the project the WCF Configuration Editor context menu will now be available when right-clicking the app.config. 

Why?  By design?  Can't tell ya...