It's much easier than you think. Most laptop touchpads run on a standard PS/2 interface, so all you need is to find out the pinout of the touchpad ribbon cable, solder some wires to a PS/2 to USB aftermarket converter or make one from an Arduino or Teensy board, and then simply hook it up to your OPi via USB and it should work as a standard HID touchpad without drivers or additional software. It'll cost you a few dollars, but it's the easiest way to do it for Android or any other OS.