I managed to successfully unlock my G&W firmware using an STM32 programmer.
Once unlocked, it's possible to compile and flash a port of the retro-go emulator collection and a handful of roms.
The emulation is surprisingly good, making the games fully playable at 60fps with sound.
Currently supports Game Boy, NES, SMS and Game Gear.
The G&W only has 1MB of storage available, but it's possible to solder a 16MB replacement instead which should allow for a good selection of roms.
Be very careful de-soldering the SPI flash chip as it's easy to lift pads and break traces. Then solder in the new 16MB chip.
Now when you re-flash the chip you can fit all the larger roms easily.. 16MB is a lot for NES games, mine isn't even half full with 24.
** All credit to stacksmashing for figuring out how to break the device open, and kbeckmann for porting the emulator.
1) Did you connect the pin without welds?
2) Is there any way to use an arduino to program it?