Palm Sounds pointed out a nice tutorial video that walks you through setting up custom MIDI mappings in DJ Player. There are so damn many DJ apps out there that I hadn't even heard of this one and it's been around since '09! I'm impressed with the feature set, including the ability to share MIDI mappings on DJ TechTools. This is clearly made by real DJs!
A brief video looking at the Midi mapping functionality in the DJ Player app from iMect. A full review of the app can be found on Digital DJ Tips here: http://www.digitaldjtips.com/2012/10/review-video-dj-player-v5/