After opening the case and having a look at the PCB, you will notice that the traces leading to the USB Mini port are easy to follow to pin on the PCB.
So if you are inclined to do this...
Cut off the Mini side of your USB cable, stripping and exposing the wires.
http://en.wikipedia.org/wiki/Usb will give you the color association you need to solder them to the PCB board.
Decide then to either de-solder and remove the USB Mini port to route the wire through that hole or whatever you decide is the easiest way.
I have done this for a friend, I ended up epoxying the cable to the PCB board in the location where the the Mini Port sat. Was easy enough to do, I am not sure if the modern Rosewill keyboards need to have this done or not.