I have looked high and low and I cant find any hack or tweak for native support. There is a lot of partial ones, but they always require a 3rd party app to go with it.I gave up.Now, I use
Pinnacle Game Profiler and it works perfectly. I had to tweak one of their existing ME3 profiles, but it works exactly the way I want it to, and its super easy to do. I also have Xpadder, and Pinnacle works SO much better than that. They have a free version, but I don't remember if it is a timed trial, or what. I know it's fully functional though. I played FEAR, FEAR 2, and ME3 with it and I was sold. It's also 50% off for Christmas right now, $9.99.
I am actually glad I found this... it even works better than native support, because you can map a "shift" button that allows you to put two commands (even the dual commands) on each button. It's friggin awesome

Let me know if you end up doing it and want my profile.
Here is my layout. The first is the standard controls, the second screen with the
blue letters is when you hold the [shift button] down, in my case, the left shoulder button.
NORMALSHIFTED