Dave, here's another confirmation of a second controller. Because of the transitory nature of my current studies and work, i needed a keyboard that had a small footprint, and so purchased an Edirol PCR-M1. It's got enough knobs and buttons to keep me interested, and importantly octave shift, and the usual pedal in, etc... I'm not sure if it has a controller map for DP (which from memory i believe you use), but it certainly works for Logic, as a basic 'control surface.' All the controls on one, and playing on the other.
Works a treat for keyswitching, and frees up the main keyboard for playing.
(allegedly, lol)
And like Daryl, the keyswitches remain constant for all instruments, which is a real timesaver, because like him, sometimes i forget which octave i'm in.
Regards,
Alex.