Edit: There are decent guides to designing and hand-wiring keyboards using computer keycaps. I haven't looked far, but something like this https://medium.com/cracked-the-code/a-complete-guide-to-buil... .
The linked layout editor (http://www.keyboard-layout-editor.com) allows pretty wild layouts. Try loading the ErgoDox layout. While you might want to go farther still, it does nicely showcase rotated thumb clusters.
The plate & case builder tool can then generate some basic CAD files for a sandwich keyboard build to fit your keys. This can then be laser cut or something.
Because most designs use a Teensy with USB connection, you might even be able to make the keyboard output MIDI, so it could easily plug into a DAW, or whatever.
