So I've been wanting a HHKB-style case for a GH60. With none of those styles around yet, I just ordered a standard dish-style case (black).
Now, I saw on one of WhiteFireDragon's youtube videos that the KMAC comes with little metal blocks to put in place of switches on the mounting plate. This would be a great solution, BUT these metal blocks are impossible to buy anywhere. (I'm fairly certain).
So anyway I had the idea to instead, mount a switch to the plate as you normally would, but purchase a key lock-out from Signature Plastics.
After installing this key lock-out on the switch, use a perfectly flat keycap, like the ones here >
http://www.pimpmykeyboard.com/marketplace.php#In effect, you have a "block" just like on the KMAC, and can take out whatever keys you want. The only problem is for a HHKB layout, you'd have to find a flat 1.25x keycap.