So, buy the real one like you do and instead of ripping it on your own, download the cracked one.
I'm not sure if fair use law says you must make your own backup for it to be a vaid backup, but, personally, if I already own a copy or two of the game, I'll pirate the roms for those versions. Especially in cases where it'll cost too much to replace the disc if it's already broken/scratched, but I would really like to finish the game or something.