Well, it's quite easy but really fiddly because the micro USB connector is very small and so are the tracks to hard wire it to.
What i did was to cut the end of the original USB lead but keep the ferrite bead in the big white blob at the end of the cable. You have to disassemble the beatstep pro so you have just the PCB then remove the USB connector, if it has not already fallen of as it did with mine.
If you look up the wiring of a USB connector they are the same for the big ones as well as the small ones so its a case of just seeing where the wires would go if the connector was in place.
The +5v is at one end of the connectors and GND is at the other end so its easy to solder those to the board, the data + and data - connectors can then be traced back to a couple of surface mount components, I soldered the leads to those but they are very small and i had to use a jewellers eye piece to see I had done it with out any solder bridges.
I cut a slot in the the plastic of the top case so then when it when back together it would drop over the cable which was in place.
All in all a fiddly arse job but it worked and the result is a fully working beatstep pro and no connector issues. :-)