If it were me, I'd start by outputting a signal on one of the PWM channels, and this would be one of the clips, and hook one of the ADC input channels to the other clip.
Then I'd see what kind of signals I read on the ADC and use some logic to determine if there was a change in resistance between the two, indicating that a connection had been made or broken. Then I'd send some data out the serial port, which is the only thing on the USB Client port.
It wouldn't emulate a mouse, unless it was emulating a serial mouse.