Title bar button to launch expose

I do usually make use of the ability of kde to move a window to ocupy half of the desktop or a quarter of it.
That rudimentary tilling ability is very useful 90% of the time to arrange your windows, but it has a cave-neat. Let’s say I want booth a firefox window AND a terminal in the down-left corner of my second screen, because that is where I put those tools I need every now and then. Now, I can do that, but I have no way to circle between the windows that are stacked in that quarter of the screen.
If I want to switch between them I have to exposee all the window, or minimize the top one or ALT+TAB, etc, but that is not a natural way to circle between apps in my opinion.
Now, I would like to see some kind of title window decoration that looked like BeOS where title did not ocuppy all window size and stacked window titles became tabs so you could choose a window under another simply clicking in the tabbed window title. But I understand this is very far reached and too many things have to be done to do it.
So today I imagined that there is another solution. If there were an Expose button in the tittle bar buttons configuration, I could add it to all the windows, so I could go to the stack, click on the expose button and choose the window I need.
Yet, there is no button that does that and I see no way to create new custom buttons.

I would like to see it implemented. The exposé button or at least the ability to create your own.

An alternative way to switch between windows would be that using the mouse wheel over the title bar of a tiled window did circle through all windows that where tiled on the same corner/half/full display place. That would be very useful to arrange your windows for easy access.

Ok, I managed to “somehow” reproduce the mouse wheel over the title bar switching by going to “system settings > window management > window actions tab” and choosing ¿Up/Down? for the mouse wheel action. Now, this is not ideal because if you keep moving down the tiled windows, not tiled windows end in the upper layer so they end up in front of the window you are looking for. Anyway, you can always make a last up wheel move to make the chosen window jump up, but you choose between partially obsured windows.