...I'd assume that since he doesn't want to mod the SFC, he doesn't want to get rid of it either.
...anyway. I had a passthrough adapter for my N64 a long, long time ago that would fit in either a US or a Japanese system and simply extended the cart slot upwards, allowing any cart to simply plug in. I'd bet my lunch money that something identical exists for the SNES.
Oddly enough, the N64 GameShark wouldn't let you use cheat codes on Japanese games. Dunno what was up with that...