If it's just for 2 weeks try cutting out anything with flour in it (bread, pasta, ready made sauces etc) and drop rice and spuds. Eat loads of greens, salads, fruit as your first meal only, and fill up on proteins, eat extra meat, fish and eggs. You'll not go hungry and if you do a little exercise you'll easily drop 7lb in 14 days. It'll be a lot of excess fluid, but then all diets do that!
Just a word of warning, cutting out flour (gluten to be precise) can make you feel like you have flu for a couple of days, it's the toxins leaving your body, so make sure you drink atleast 2lts of water a day to flush them out.
Good luck :o)