The PS Joy Converter (USB), manufactured by Boom, is just that solution. While there are handfuls of these types of devices, this is the only one I have found is truly plug-and-play and works perfectly in conjunction with software such as USB Overdrive or (even better), GamePad Companion.
I ordered two, and when used in conjunction with GamePad Companion, two-player gaming is supported. I purchased mine from lik-sang.com.
Highly recommended!

