Seeing as this is basically a variable resistor, I'm sure you could attach circuitry that would turn it into a digital one or off based on the resistance, and thus be suitable as a momentary switch. Many things could do this, such as a microcontroller.
A cheaper - $7 method uses a chip that could easily do this easily, the LM series used in the HD indicator mods. Just attach the touchpad onto the 5V Molex and the analogue input, and set the 10th LED output to an optoisolator, and a XOR gate. You'd loop around the input from the end of the XOR to a 5 uF cap and the optoisolator back to the other input. This would allow you to both turn on the computer and turn it off with the switch. You'd then adjust the resistance values on the LM for that of the touchpad. You could also hook up the other 9 LED outputs for a cool display on the front of your case.