There's a method to turn USB power on which is probably not persistent. I hope this will help you.
echo 0 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio0/direction
echo 1 > /sys/class/gpio/gpio0/value
echo 0 > /sys/class/gpio/unexport
At this time, you can add these code to /etc/rc.local for your convenience, which should be executed once the system init finished. But pay attention to the system upgrade which could overwrite this file. I will contribute a kernel patch in order to make this change persistent soon. You can mark this topic as [Solved] when your problem is solved.