I’ve found this – https://www.dropbox.com/help/89/en, but it apparently only works with DropBox for Business.

For normal DropBox, what I’ve done is (on Mac OS X) :

• Quit DropBox App
• move /Users/KD/DropBox to /A/Sync
• ln -s /A/Sync /Users/KD/DropBox
• Start DropBox App

So far seems to work fine.