I mounted a Holosun HS510C red dot sight to a bug-a-salt. A single pump builds compressed air which shoots out table salt for killing flies and small insects. It's hard to aim when they're flying, but the red dot helps.
3D printed adapter that fits the mounting pattern, the wedge shape goes in the side under a lip from the injection-molded plastic, locking it in place.
View of the red dot
The 3D printed block the site is sitting on snaps gently in place but sits fairly loose, so I had wedges that get pressed in from the back to hold it steady.
CAD of the mount base, optics-trade.eu provided the mounting pattern
Underside of the mount base. Small counterbores for mounting screws from the bottom.
Wedge for inserting under the lip of the mount base, friction fit holds it in place.