First off, you will want to remove the arm rest, and remove all visible screws on the bottom of the keyboard. There aren't any hidden screws underneath the rubber feat, however there are two hidden screws underneath the label placed on the back. I have marked them in red on the image below. Some how I missed these on my first pass of all of the screws and took me about 30 minutes to find these hidden screws.
After removing all of the screws, you can start attacking the case with a sprudger. I highly recommend buying some if you don't have any. You can pick a pack of 5 or 6 of them up on ebay for about $6, and are well worth it.
NOTE: This should go without saying, but opening your Truly Ergonomic Keyboard will void your warranty.