You can pretty much use any MIDI device to tell the Whammy what setting it should be on. Either a small keyboard controller or MIDI pedal.
The unit comes with a MIDI chart...
If you don't have it, here it is
http://www.digitech.com/ftp_mirror/PDFs/Manuals/Whammy.pdf
What is happening is that you are pretty much making presets with dedicated channels for different settings...
IE:
MIDI channel 1=Detune shallow
MIDI channel 2=Detune deep
MIDI channel 3=Octave up
Etc.....
In MIDI, you program the controller so that a button or a key will send that message to the pedal. This is done via the controller, not the whammy pedal.
It's very simple to do.
It's pretty much just like hitting a button.
So if you are going to use a keyboard, you will have to know how to program that keyboard to SEND a MIDI signal.
Get out your trusty owners manual for the keyboard, or download it if you don't have it. And read up on how to assign a MIDI channel to a specific key on the controller.
Then just plug it into the Whammy, and you are done.
Let me know if you need more guidance.
Steve