TV and radio stations have a set amount of time for commercials within each show. When stations aren't able to sell all the spots, they often fill them with PSAs from the Ad Council. You could work with the Ad Council to produce short (30- and 60-second) exercise videos. The spots could encourage the audience to start moving, plus give them exercises for the 3 minutes *after* the commercial. TV stations might appreciate that viewers would stay in front of the TV doing the exercises during subsequent commercials, rather than wandering away.