Obidience Issue -- The Bedroom Window

We are having a major training problem with our 9 mo. old lab, Dawson. We converted a den into a bedroom and it has floor to ceiling bay windows that Dawson loves to sit in front of all day and watch the neighborhood activity. Unfortunately, when he sees a friend (or enemy) he likes to jump up against these windows (in the process, destroying mini blinds). Our biggest concern, however, is the force he hits the windows with, we think he's going to put a paw through one of them these days. Fencing and gating this room isn't practical.

Any training tips for curbing his enthusiasm about the dogs going by outside???