Is there any material that obstructs or resists capacitive sensing?
Interpose a conductor - a sheet of copper, or tinfoil - between finger and capacitive touch sensor - and ground the conductor. (It must be insulated from the capacitive sensor, of course). 

Your finger will form capacitance to the ground plane but not the sensor behind it.

This assumes the sensor reacts to changes in capacitance, not absolute value, otherwise it will simply see a large constant capacitance to ground...