Here's another shot of the Pokéball I recently built. It's constructed very similarly to my Lego Wheately. You can download Lego Digital Designer files right here: Lego Pokéball.
You'll notice that the internal structure is quite dense. It's certainly possible to design the ball to open, but it hampers the overall structural stability, and so I decided against it. I haven't caught a Lego Pokémon yet, anyways. :D