Converting USB 3 cord to 20 pin MoBo connector

I've got a Crosshair V Formula MoBo and a Corsair 600T case.
The case has a front panel USB 3 port and the plug is just a long USB cable that snakes through the case and plugs into the back.
The motherboard also has a 20 pin spot for USB 3.

My question is, how can I convert the case USB cable to the 20 pin connector so I can use the front panel port and the rear MoBo port at the same time?