Get this device from Thinkgeek called the "Annoy-A-Tron" and plant it in his office. Have fun.

http://www.thinkgeek.com/gadgets/electronic/8c52/

It is a device that emanates periodic beeps in irregular intervals. The frequency is such that humans cannot locate the direction of the sound. It will drive him nuts.

"Life is like a bicycle, if it's too easy - you're probably going down :)"