Oh, what a fun project!! Having them meow for a treat is a good suggestion, and can be learned fairly quickly

One thing that we taught one of our cats to do was fetch! Scooter, believe it or not plays fetch with us. We started out with a tinfoil ball, since he had a tendency to play with them anyway. When he would drop it somewhat close to one of us, we would reward him, usually with a treat. Eventually he was bringing it right to us!! A pretty cool trick, because people usually associate that kind of behavior with a dog. The only difference is in the way cats and dogs are motivated. Dogs are motivated by the urge to please a pack member (ie humans), whereas cats are motivated to please themselves! LOL LOL

Good luck and let us know what you do!