There are (or were) some simple non-jailbreak hacks for older Kindles but I've never found one for the Touch. This is one thing that really pisses me off about Amazon--they don't seem to give a darn about allowing us more control over things like margins. For me the smallest margins are too big on a 6" reader, but they are ridiculously huge on a iPhone or smaller type screen. This is one of the things many have complained loudly about for years but Amazon just ignores us.