Hi,

I did a small demo in the style of SMB once that (I think) does what you want to do; you can d/l the source file at http://creativecoding.uni-bayreuth.de/assets/Uploads/GameDesignAssets/supermonkeyball.zip.
The demo is designed for the XBOX360 gamepad but you can easily replace the joy_ variables with key_ equivalents. If you cannot use the environment glass shader for the transparent ball, just delete/uncomment the lines for the shaders (e.g. "#include <mtlFX.c>; and my.material = mtl_envGlass;).
Hope this helps; let me know if you have questions regarding the code.
Best,
Stefan