Burt, this is great! Love that the idea works with the environment in which people find themselves while watching television. Your idea not only promotes exercise, but in a world where businesses often value monetary gains over people this also gives brands the opportunity to "sale" their brand while placing them in a good light. Application wise, your idea would be fairly simple to implement.
A thought I had while reading your idea: What if there was an app available that could be used to keep track of people's engagement while rewarding them for their participation. Rewards could vary from badges, displaying username high scores while the commercial breaks are happening (motivator for those who like to stand out), to partnering with local businesses to provide discounts or awards to those who complete a certain amount of exercise routines. Now that I think of it, FitBit could be a great partner in this endeavor. They already monitor heart rates and calculate how many steps people take.
OpenIDEO, might be worth the try to pitch this idea to them.