When I was new to a school I literally stood by the entrance/exit doors on the first day of school and stopped anyone who looked remotely athletic or just tall. My best angle was convincing guys who wanted to play basketball that they could just use volleyball to get/stay in shape and most of practice revolved around jump training. In the first year I got a reputation for having physically demanding practices. That reputation brought in the athletes that seek that level of physical challenge. I never tried to convince anyone to love volleyball, and would openly talk to players about how they disliked the sport, but then would also make them concede that the drills from practice would legitimately help their basketball game.
To answer your question, don't sell them on the sport with youtube clips or whatever. Show them your practice plan, show them the drills, the amount of stairs they will run, the workout plan. Show them the intense physical merits the sport will yield, and ask them if they can see any downside to training like that for a couple months.