Guess I'm a fucktard, as S.Campbell would like to say :P
That's some bloody strange thing going on in there. That means the Megadrive has to be added, but NOT just any adapter. My example on SuperGameboy still remains, and there's also some addons for the PSX to play GB games and others.
There IS a NES to SNES addon, do you reckon it would work in a similar way to the Genesis thing?