Here are instructions for finding him, courtesy of Travis Ogdon:

"On the Boston level if you ollie through the glass windows on one of the buildings (it's one or two to the left of the one where Ben Franklin is hiding) you land in a living room with a flat panel tv on the wall. If you stand in front of the TV Ghyslain gets up and shouts something about watching Star Wars (which you're now preventing). Hitting O (on the PS2) will result in him showing off his moves."