I just bought the 600ex a week ago from them. Are you f'n kidding me???
buy another one at the new price, get an RMA for the old one and return the new one that you receive with the information from the old order (assuming they were both refurb purchases).
I had this happen a few months ago with 70-200 F/4L IS where it went on sale literally 2 days after I bought it for $250 cheaper. They would not issue a price adjustment, but they basically said to do what I said above, worked perfectly.