Also the CC runs off of vacuum and doesn't work or know what to do under boost, that was my understanding of why it isn't used on the boosted cars.
you just need some type of vacuum accumulator. (or electronic throttle) when you are running cruise control, chances are good that "IF" the engine goes into boost, it will be for a very short time. even at 0-psi on the boost gauge, you would be pulling pretty hard to keep your speed steady. there are many other cars with turbos that also have cruise. mazda just decided it wasnt needed on the MSP.