If your son was invited to Jr Nationals, then he's already getting plenty of exposure. However, I see very little down-side to putting together a short video and including a link to it with all of his e-mail correspondence. If the coach thinks it's an inconvenience, then he can ignore it.
Most of the "standard" pitcher videos that I've seen from PG showcases are about 30 seconds long, shot from the pitcher's throwing arm side. You can shoot your own video and add any of these options:
- view from behind the mound
- titles for his different pitches so the viewer can compare arm slots
- stretch and wind-up
- gun reading if you have one and if the number is impressive
- slow-motion sequence for one pitch
- live game action (what does he look like in a big game)
Just some ideas, but it doesn't have to be fancy and should only be about 3 minutes long. Also, include all his contact information in case someone finds it on their own.