I found this funky little box for $20 at a used music store that translates incoming MIDI signals across channels. I don't remember what it's called, and it's down in the basement. If I find it I'll let you know what it's called.
MIDI Solutions makes these two products - either one is $150.
http://www.midisolutions.com/prodevp.htm
http://www.midisolutions.com/prodrte.htm
I guarantee you that it's possible to do this cheaper with an arduino (or any microcontroller).
As for mods to the keyboard itself, I did this, to put the touch strip in permanent pitch-bend mode:
http://kineticturtle.blogspot.com/2011/
eytar.html
I have plans for more, including reversing the touch strip (so it goes the normal direction), and eventually making a sustain control. There may be a writeup about how I use the rockband keytar live soon by someone from Harmonix.