What's an effective way for me to lose 40 lbs when i can't have any pressure on my feet?

Low impact: Swimming is probably the lowest impact exercise you can do to lose weight--riding a stationary (or nonstationary) bicycle puts some pressure on your feet, but not as much as running or walking would. Weight training also burns lots of calories--upper body would probably be more applicable to you. Also, nothing better than diet--cut out sodas and high calorie snacks, etc.

See below: Sound like you will have to rely on a diet. You can still do upper body workout and some lower body with using only your legs and not your feet.