The old physx (2.8.x) has this feature in which you can disable collision or notification within group. Eg disable collision between custom trigger with all other objects and this can be done as long as you have the object physics handle (in 2.8.x it was NxActor, it is probably the same thing too in 3.x).
You will also need to link to physx library directly.
All in all, it is most probably doable (havent tried it myself) without modding the engine source.