I happen to have a board from my FunnyPlaying build so I figured I'd give it a shot. Used enamel wire to make the button contacts and got 3.3v from the cart slot. I also removed the caps as to not power any circuits that didn't need (CPU and RAM were donors to the other board). Power is provided via AA batteries.
There are and they work very well(3ms latency). No mods required . https://shop.insidegadgets.com/product/wireless-gameboy-controller/
That's sick as hell