I've been thinking these small tie clip style microphones are probably the best option for placement in the tea cups. I'll need four, each connected to the small mixer and then to the computer. I think the fact the they will be inside ceramic tea cups will color the sound interestingly and add to the sonic experience for the user.
The use of contact microphones instead of standard clip type mics is something I've been thinking about. This would certainly have a massive effect on the sounds being played/spoken into each cup but might detract from the users understanding if the sounds were changed beyond recognition. I'm going to purchase a cheap, small, contact microphone this afternoon to experiment with how it colors the sound I make into one of the tea cups.