Default [Q] Capture Stylus events before they go to Apps

Reposting from where I previously put this, on the suggestion that folks here might have more idea what I am talking about.
Yes, this is a question but I couldn't see that it fit in better to one of the other forums. If I am wrong please accept my apologies and redirect me, thanks.

I'm trying to work with a custom build of Android based on KitKat to incorporate a stylus, copying some of the functionality (though not code) from Samsung which sells Android-with-stylus builds for e.g. the Note 3. I'm not including details of the specific device because right now I am working on a custom dev device and my aim is to write code which is generic enough to be usable from any Android (based on KitKat). The build (written by others) already incorporates drivers and sends stylus events correctly as motion events etc. Programming at the app level I can receive onHover, onTouch, onClick etc

The specific functionality I am trying to achieve is to pick up a stylus-button-click while hovering. It's perfectly possible to do this in any app, using an onGenericMotion Listener.

However, I want to make my "stylus-action" have system-wide effect - so that anywhere (in any other app, or in the launcher or whatever) I will pick up the event (prior to any other app) and bring up my custom menu. (just like AirCommand in Samsung Note 3) I guess in my custom Android this would then make that particular action somewhat protected or unusable for other users, but I'm ok with that.

In older Android (prior to ICS) you could try something by putting up a System Overlay (i.e in regular app code, without hacking the ROM at all), but this is no longer possible.

This is not an attempt to tapjack or whatever, I understand why this functionality has been removed from the domain of the regular programmer, and I don't want to regress my ROM back to pre-ICS behaviour by allowing the System Overlay hack. Now I am programming the system (if my change is good enough I'd like to submit it back to AOSP) so I would like to know the best method to address this. Since Samsung have already done this, it must be legal (using legal in the terms of "Android will allow it"), and I want to do it right.

Is it possible to write something similar to the System Overlay when you are running from a system service? Or is there a good choke-point to capture events before they are broadcast to the current running apps?

I was looking at (sorry, not allowed to post links) AndroidXRef /frameworks/base/core/java/android/view/View.java specifically in the function dispatchHoverEvent() which looks like a promising place. My naive idea is that I would place code here checking the MotionEvent to see if the button is pressed and if it is, don't call any listeners and instead call my little menu app (or broadcast a custom message, or something anyway). However, I've never written code on the ROM level before (LOTS of experience writing app code) so I don't know if this is a really bad point or a good point to add in code. Should I be putting things at a higher level or a lower one? Will this capture all events or not? Is it all just trial and error?

If this is the wrong place to ask questions like this, please tell me where on XDA I should be asking it. If it's the right place - please answer

Thanks
Kibi