The only thing I can think of is natural diuretics, like dandelion extract, dandelion leaf tea, nettle leaf tea, green tea, cranberry extract, and fennel. The best diuretic is water, so try to up your water intake to 3-4litres per day (spread over the day, do not consume a lot of water in a short time). Avoid salt and sugar, as they help retain water.
I doubt cutting down your shakes would work, as you risk going into starvation mode.
Only other thing I can think of is to go for a full body wrap just before you go to the hospital, as they are supposed to make you lose a few pounds but only until you start drinking fluids again!