open a your command line and navigarte to the SD card on your phone (type E: F: etc)
Now type in each of these below
fsutil file createnew testfakedb01.jpg 2147483648
remove your phone, then plug back into your computer once you do click on import to dropbox from the autoplay settings, this will upload a 'fake 2gb picture to your dropbox account' and for doing so Dropbox will reward you with the same bonus space. u can repeat this process up to a max of 3gb (it used to be 5gb) just make sure you change the file name from 01 to 02 03 etc (i've typed two below 650mb and another 2gb)