I got the Switchcraft Panel Mount Connector - USB B to A in sweetwater
http://www.sweetwater.com/store/detail/EHUSBBAB/, and ID INNOVATIONS MULTIMODE USB ADAPTER sold by mkawa
http://geekhack.org/index.php?topic=48030.0 I used the USB adapter intact, so I can replace it later If I wish.
Step 1: open the keyboard:
step 2: remove the cable from the casing, and use a step drill to make a hole until the USB connector fits
step 3: mark the areas for the screws to be drilled
step 4: drill the holes
Now, since the original screws had no nuts, I had to replace with something I already had at hand. Luckily, found some black screws that fit on some type of nuts
Step 5: Screw the panel from the inside