[If this is not what you were wanting to hear, ignore me]
Ok, so assuming it has a triple with a 52/42/30 and a 12-26 cog that would put your low gear at like 31 inches or so. If you can replace the 30t chainring with a 28 and the cogset with something that has a 34t for the low end then you'd have a 22" low. Wayyyy better. If you can, see if someone with about a 22" low can let you borrow it for a sec to try it. Go to your LBS and ask to test ride a bike with really low gears. I think you'll forget all about this weight thing and see you just needed to gear it to the hills and weight you have to carry. This answer is simpler, cheaper and more practical.