Dell R720 + 6 pin pcie power

I have a dell R720 and a pcie card that requires a 6 pin pcie power source.  The only thing I see inside the dell case for power is an 8 PIN connector on the riser card. 

What's the recommended way ( or even better .. part number! ) to get power to PCI cards that require a standard 6pin pcie power source?  

Thanks