Surfing: Did you read the manual? "To end your ride cleanly, go over the top of the wave just before time runs out."
Flying Disk: I didn't state that well. You get a lot of points for distance thrown. That's why the overhead catch doesn't work. So you have to do a diving left catch since that allows the disk to travel the furthest. You're not catching it behind your back, just turning back to do a diving left catch.
It's pretty hard to do and it came down to chance for me. Keep trying it and eventually you'll get lucky, that's the only advice I have.