if the psu doesnt have any molex cords or a 6 pin sata connectors, i would think you are out of luck with the psu(and the psu probably isnt built to handle the gpu if it doesnt have either)
the only choice to getting a 6 pin that i know of is having a 6 pin on the cpu, or using a double molex to 6 pin convertor if you have a molex cable being unused.