I installed classicube on my xperia play, and it runs ok at ~25fps, but the buttons don't do anything. I would really love if the xperia play was fully supported.

ClassiCube doesn't have any kind of native controller support except on the console ports, and as far as I know, there aren't any easy to use libraries for interfacing with the Xperia Play's buttons, making the possibility that this could be developed extremely low, unfortunately.