JD has drawings for acrylic spacer layers, but i'm leaning toward spacers on the fasteners. i'm kind of tired of layered acrylic, even if they're just spacers, and spacers on the fasteners allows for building an angle into the keyboard itself.
further, the spacers could be made out of cut to length polyelastomers: sorbothane carries bushings in various lengths as stock items, and polyurethane extrusions are inexpensive as well. energy absorbing PU springs instead of rigid polycarbonate, and titanium instead of aluminum would make for the deadened feeling of a large heavy keyboard in a very tiny and light one.