Best way to do that is install GameEx on your C: drive (default C:\Program Files\GameEx whatever), configure it, then copy your GameEx folder to the HDD. Then on his side, he can install GameEx on his C: too, then he can just copy over his GameEx folder with your one from the HDD. And if you have all the ROM paths and emulators set to E: and he sets the HDD to E: also that should be all you need to do.