The tool I used for it is called the Retrode2, a cartridge dumper which doubles as a 2 SNES and 2 Genesis controller hub.
With a bit of patience you can even run SNES carts on a Steam Deck https://mastodon.social/@16bitvirtual/116479936082268893
Is it cheap? Nope
Is it sensible? Absolutely not,
Was it fun? 100%
The most frustrating accessory ever...
I can't remember how well it worked as a mouse, but "Mario paint" felt the same as any PC paint.
Playing single player using a mouse in one slot and a gamepag in the other hand could have been amazing.
But even just "point and click" or strategy game.
The mouse was great just a giant waste and that's why it was so frustrating
I got that before I even had a PC mouse. It blew my mind.