My job has me use lots and lots of aerosol spray lube, and using that for hours at a time will cramp your finger, then your thumb, and then both.

Most options for this kind of handle attachment connect to the small collar nearer to the nozzle, but that design leaves very little plastic to grab on to the can, and inevitably wears out. This attaches to the larger outside diameter of the can, giving it a lot more of the can to grab onto, and a lot more plastic to wear against.

The necklace part and the handle must be printed in 2 pieces and glued together. Super glue (cyanoacrylate) works great for this, at least with PETG filament. Use and old machine screw or wood screw for the trigger pin, hell use a piece of filament, it'll probably fit.

I'm including the FreeCAD documents for this in case anyone wants to modify this design for their own purposes.

This won't fit non-standard diameter spray cans, and some spray cans are designed differently near this collar. it will stretch to accommodate a bit, and if your can is a little bit too small, a wrap or 2 of electrical tape around the 2 fingers of the necklace part will take up the gap and make it very satisfying to use.