It will be fine, just make sure the red wires go to the USB_PWR pins. If you are really worried, use this extension, you will only need one, and it only uses 4 wires per port:
APEVIA Model CVTUSBE25 - Newegg.com
But if you are planning on mounting a box externally, why not just get a USB hub. Neater, cheaper, 5 more ports, and free shipping.
Rosewill RHB-320R 7 Ports USB 2.0 Hub with Power Adapter - Newegg.com