OK, so after having a look at how things work, I've marked out 1 possible method. It's such a simple idea too.
In the images below I've marked out for 2x slots to be cut into the back cover where 2 free running, shallow head screws will slide.
They will pass through the slots and screw into the actual keyboard below, hopefully not damaging anything inside, (maybe contact Dirk, Kimmo or Andrew to find out what's in that big space at the top of the keyboard).

Keeping the original circuitry intact should negate the need for bluetooth as it should connect through the original TOHKBD software.