Macros for 360 Controller?

I use an Xbox360 controller for gaming (with the default Microsoft drivers, etc.). I'd like to set up some macros so that when I hit certain combinations on my controller sequences of controller inputs are sent to the game (instead of the input those buttons would normally send). For example, when I press back+X I'd like the game I'm playing to receive the input A, B, A, B. Is this possible?

I can easily set up behavior like that in games that DON'T support a 360 Controller. For instance Pinnacle Game Profiler makes setting it up pretty easy. However, if I use the same method in a program that DOES support the 360 Controller then when I hit back+X the game receives the input back+X, A, B, A, B, instead of just A, B, A, B. I'm just adding things on-top of the controller's default functionality, not replacing it.

The game I specifically intend to use this for uses every single one of the controller's buttons, so I can't just employ an unused one for my macros--there isn't one. Also, while the program also accepts keyboard input, it won't allow mixing and matching keyboard input and controller input. Otherwise I could easily do what I want by assigning in-game functions to keyboard keys and then using PGP to make the buttons send keyboard input in the appropriate way.

Does anyone have an idea as to how I can make this happen?