Let me test my understanding: what you want is an event dispatcher, i.e. a function/procedure which responds to *all* the form events, does whatever it needs and then calls the proper event handler, if any. Is that it?
I don't think that will be easy. Your best bet may be setting a kind of message-loop like that in TAplication but AFAIK TCustomForm hasn't any facilities to do it easily.
Let me sleep on it and maybe I can think of something.