I reckon AerBabe's suggestion is the right one. Sit with another keen pilot (or friendly ATCer) and pretend you're on a long and complicated routing. Do all the chat for real (and hope the other person can give you some tricky situations to talk your way out of). I learned morse by a similar method aeons ago, and it stuck.
Reciting car registration numbers will teach you the NATO phonetic alphabet, but you need something more "real" for the procedural stuff. Live practice every time! With CM you'll learn the right way and quickly; with AB you might have more fun but probably learn less RT
Or sit in the back seat with a couple of experienced lags on a trip. If you were in the South East, I'd have a suggestion for Wednesday.