Is it possible to make custom OSX Player windows in Unity?

I'm interested to know if it's possible to customise the Mac OSX Player window in Unity, similar to what is seen here: http://www.cocoawithlove.com/2008/12/drawing-custom-window-on-mac-os-x.html

As described in the above tutorial, customising the window seems simple if we can access to the main NSWindow for the app, but I've noticed that Unity doesn't make an Xcode project for Mac OS builds. Would a native objective-c bundle/plugin be able to access the main NSWindow object of the OSX player? Any help you can provide is greatly appreciated!