Do you need the other sprites you want to pass through have the platform behavior? If you need it just for gravity, you can do similar with the bullet behavior.
The other sprites need the platform behavior becuase they is supposed to move up slopes and move on platforms that aren't completly flat. They are just not going to stopped by the platforms the player sprites is standing on. I suppose i can make still give the other the bullet behavior and make them move in the directions they would move in whit the platform behavior. But i still would want a another answer so i don't have to do that.