Adding a button event handler to a child window in G4P

I've noticed that none of the examples with G4P feature working buttons in external windows (created using the GWindow factory methods). I've also noticed GWindow has no addButtonHandler() to go along with addMouseHandler() and addDrawHandler(). What I want to know is, how do I get a GWindow object to handle button events without making my own implementation of GWindow? Surely there is some simpler way that I am missing? The same goes for slider events and other such things, since I'm sure I'm not the first one to want functioning UI widgets in an external toolbar window.