Pool running can give you a serious workout, and since you probably don't want to risk anything that will aggravate the foot, maybe you should just bite the bullet and focus on that for a while. Don't risk trying something that ends up extending your recovery time by another 2-3 weeks.
As for keeping your weight down, just pay closer attention to what you eat. I was in the same situation a couple of years ago (not a broken foot but couldn't do any kind of aerobic exercise) and focused on cutting back on the little things. For example, except for my morning cup of coffee, I drank nothing but water, even with meals (a 16 oz bottle of fruit juice drink packs about 200 calories). I eliminated cream cheese from my morning bagel, and switched from mayonnaise to honey mustard (fat free and very low calorie) on sandwiches. I don't like chips and fries to begin with, so that wasn't a problem. Wherever I could save a few claories throughout that day, I did. Substituted salt and pepper for butter on vegetables. Ordered sandwiches without cheese. Stuff like that. I still allowed myself snacks and desserts and stuff, but just tried to be smart about what I ate. Good luck!