I have just unplugged a solenoid that controls the valves in the exhaust, making the car permanently loud. It took about 1/2 an hour and costs nothing. Here is a thread I found after much searching, there is a step by step guide.
http://www.lamborghini-talk.com/vbforum/f25/gallardo-loud-standard-exhaust-11503/
http://www.lamborghini-talk.com/vbforum/f25/gallardo-loud-standard-exhaust-11503/