mm, it would be easer if it was made of some kind of plastic. Then you could just paint multiple conducive areas in it. I think you might run into problems if you have to many, Atmel do a chip for multi dimensional conductive arrays and it sorts out a lot of the cross talk for you. I am going to tackle one when i have the time, i thought of using transparent conducive plastic layered with non conduction transparent plastic and then all put through a laminator to make transparent-ish conductive switched. Anyway your object is metal mmm. lot's of small microphones and some fancy code? piezo microphones stuck to the inside?