I used to have a few of them but sold them all.... I'm not sure what they are called but they were tiny cartridges (about 1/4 the size of a normal NES cart) and you could play any region NES cartridge on them (y) I know as I used it ^^
yes, Game genie is not endorsed by Nintendo (even sued back in nes days) meaning they bypass the 10NES chip, however i do not know the steps in witch it boots the retail games plugged into it, i know how the cheats work. I DO NOT RECOMMEND USING A GAME GENIE!! it will damage ur nes. look it up.
Personally i would just mod the hardware as suggested above with a good pair of side snips.
i hope you also know that regardless of how you do it, some out of region games will have bad glitches on out of region consoles.