This is the first plan that seems actually good enough to try.
4 pc aluminum (or other) tubing with a matching diameter Drill bit. On my rig, the short rails are 8 1/2” and the long rails are 22 1/2” but you can adjust this to best fit your application.
1 Ikea Boholmen plastic cutting board or similar
A small piece of foam for the shoulder pad, if desired.
Several small screws or nuts and bolts with drill bit (and tap if desired) to match
2 bicycle hand grips
The parts scheme as a downloadable PDF or png file