Years ago I wanted to play some classics on my computer at work but couldn't bring a wired controller to work as there was no port to hook to. So I tried to make my own joystick that could be strapped to the numbered keys that would allow it to push the up/down/left/right keys.
I drew the joystick up in cad for fun really as I already knew I'd be using an old NES Advantage joystick that had broken years before. I wanted the stick to be adjustable to most/all keyboards so I made the contacts to the keys out of machine screws with felt heads so that they could be adjusted up and down. Once the joystick was on the keys it couldn't move because the sides of the stick rested against the keys borders and could be either strapped down or held with a couple large rubber bands.
I built a prototype of my stick by cutting apart a NES Advantage joystick and attaching sides of foamboard. I also tapped some contact holes to place the adjustable screws into.