How to make an entire (irregular) surface sense touch with a capacitive sensor?
Usually you would etch the capacitive switches onto a PCB, but with an irregular surface some aluminium foil glued to the back of the surface (with wire from foil to capacitive sensing circuit) should work fine.
The larger the area and the thinner the insulating surface material the better.  

A uC like the PIC16F1828 would be good for this application, they have a capacitive sensing peripheral with something like 8 (maybe more) channels.