Best thing? Use NGUI events to start with. Don't process Input events yourself. NGUI does a full range of events for you -- press, click, drag (move), drag enter / exit, etc.
Keep in mind that fallThrough object will be receiving all those NGUI events if nothing else does.
If you can't do that, you might need to expose UICamera.mTouches so you can loop through them yourself... but I wouldn't advise it.