I've gotten some more time to fiddle with GObject/GWidget and to try getting the signal/slot mechanism to work properly.
Now it seems to work, you can test connections and actually call 'em. The pointer can be of another class, e.g. a GObject pointer can dispatch signals in a GWidget object without knowing of them.
It seems to be possible to automatically generate code that works with this. I've tried with the Bin, Container and Button classes and got it to work without too much tweaking.