MCP23S17 and Capacitive Sensing

Projects Programming
1

I have ~90 'touch buttons' (an electrode with two cables and a 1 MOhm resistor, I need ~91 digital I/O pins) which I want to operate with the CapSense library. The issue is that I don't have enough I/O pins to do this. I did some research and found out that a chip like the MCP23S17 (library) can extend the number of I/O pins, but I am not sure if it works in combination with the CapSense library.

I know you can easily replace things like DigitalWrite, DigitalRead and PinMode with the MCP23S17 library, but I am unable to replace the code below:

(File: CapacitiveSensor.cpp, CapSense library)
(...)

sBit =  digitalPinToBitMask(sendPin);			// get send pin's ports and bitmask
	sReg = PIN_TO_BASEREG(sendPin);					// get pointer to output register

	rBit = digitalPinToBitMask(receivePin);			// get receive pin's ports and bitmask
	rReg = PIN_TO_BASEREG(receivePin);
(...)

    noInterrupts();
	DIRECT_WRITE_LOW(sReg, sBit);	// sendPin Register low
	DIRECT_MODE_INPUT(rReg, rBit);	// receivePin to input (pullups are off)
	DIRECT_MODE_OUTPUT(rReg, rBit); // receivePin to OUTPUT
	DIRECT_WRITE_LOW(rReg, rBit);	// pin is now LOW AND OUTPUT
	delayMicroseconds(10);
	DIRECT_MODE_INPUT(rReg, rBit);	// receivePin to input (pullups are off)
	DIRECT_WRITE_HIGH(sReg, sBit);	// sendPin High
    interrupts();

	while ( !DIRECT_READ(rReg, rBit) && (total < CS_Timeout_Millis) ) {  // while receive pin is LOW AND total is positive value
		total++;
	}
	//Serial.print("SenseOneCycle(1): ");
	//Serial.println(total);

	if (total > CS_Timeout_Millis) {
		return -2;         //  total variable over timeout
	}

	// set receive pin HIGH briefly to charge up fully - because the while loop above will exit when pin is ~ 2.5V
    noInterrupts();
	DIRECT_WRITE_HIGH(rReg, rBit);
	DIRECT_MODE_OUTPUT(rReg, rBit);  // receivePin to OUTPUT - pin is now HIGH AND OUTPUT
	DIRECT_WRITE_HIGH(rReg, rBit);
	DIRECT_MODE_INPUT(rReg, rBit);	// receivePin to INPUT (pullup is off)
	DIRECT_WRITE_LOW(sReg, sBit);	// sendPin LOW
    interrupts();

#ifdef FIVE_VOLT_TOLERANCE_WORKAROUND
	DIRECT_MODE_OUTPUT(rReg, rBit);
	DIRECT_WRITE_LOW(rReg, rBit);
	delayMicroseconds(10);
	DIRECT_MODE_INPUT(rReg, rBit);	// receivePin to INPUT (pullup is off)
#else
	while ( DIRECT_READ(rReg, rBit) && (total < CS_Timeout_Millis) ) {  // while receive pin is HIGH  AND total is less than timeout
		total++;
	}
#endif
(...)

Does anyone know how to do this / know a better alternative?