I'm not a CapSense expert, but I think you should be able to do this by collectively connecting multiple pins to the Analog Mux Bus (AMUX). This will let you short the pins internally.
Use the MUX_CRx Registers to short pins to the AMUX. After you should read the Rawcount just like you would do for a normal sensor. The difference now will be that you'll have increased sensitivity.
Hope this helped. If you have any doubts let me know.