As far as I know there's no definitive answer yet. I guess we're waiting for someone to actually obtain the required cable and successfully fit a second drive in a 2011 mini with Radeon 6630M. It certainly looked like there was room in '''mine''' when I fitted my SSD the other day. It had the space under the HD just like in the teardown of the Intel-graphics-only mini. As soon as it's confirmed possible I'll be adding a second drive to mine for Windows.