I'd thought I'd also explain how this is going to work...

The Ninja* replaces the ROM inside a Game Genie cartridge, allowing the user to execute whatever is on the rom. When the Ninja* is started, it either enters "Play" mode if any controller buttons are held down on startup, or waits for a transmission from the PC. The PC would then send it 2048 bytes (to RAM), and then execute that. From there, 3 things could happen:

1)A homebrewn test would execute (ppu/cpu timing, sound, etc.)
2)The RAM code would set it into "Play" mode, and execute the game.
3)The Genie could be set into "Play" mode, but the game not started, giving the RAM code full access to the cartridge hardware. The cartridge could then be dumped and transfered back to the PC, or the PC could transfer data to the NES, which could then be written to WRAM or a SRAM dev cart.

In this case, It would be cheaper than most other solutions, but would be significantly slower. Then again, it's another easy [!] solution.