The answer, in this case, is updating the CUDA driver manually. Finding the driver, though, is non-trivial. For instance, this page says that there are no drivers available for the mac. To find the CUDA drivers, you need to find the Developer Zone, and go to the CUDA downloads page. Interestingly enough, the Getting Started Documentation (pdf) is Windows specific and does not include the 300 series in its list of supported cards. However, downloading the CUDA for MAC drivers works just fine on my machine. Note: you only need to download the drivers (currently the middle of the three links) to get it working.
CUDAQ (* True *)
CUDADriverVersion (* 4.2.9 *)
alongside the rest of the tests. But, the proof is in the graphics:
data = CUDAVolumetricDataRead[
CUDAVolumetricRender[data, "Width" -> 400, "Height" -> 400]