Sorry, I forgot to "backwards-check" my code, my suggestion will not work until the next release.
The mouse down event does reach the button, but in Vip7.4 (and earlier) you will have to attach a native event handler to get it.
Normally, I would not recommend extending standard controls with unusual features (because people should get the behavior they expect), but here we are not using the button as a button: we are using a button to "fake" something completely different.
The focus listener will be invoked whenever the button gets focus (obviously).
I guess that this can only happen if we right click the button. Other potential ways would be if we TAB to the button, but I don't think these buttons should have tab-stop. Left-clicking also brings focus to the button, but since we destroy the button on a left click I guess the focus event will never arrive.