How to define completely new xdg-user-dirs?

I've just configured my ~/.config/user-dirs.dirs file under unity (ubtuntu 12.10) and everything works well so far. But is there any chance to extend the user dirs like this:

XDG_UBUNTUONE_DIR="$HOME/Ubuntu One"
XDG_DROPBOX_DIR="$HOME/Dropbox"
XDG_TEMPORARY_DIR="/media/SYSTEMDATA/Temporary Data"

As you can see I want to define completely new entries. How can I define them and e.g. specify icons for those new entries?

THX BKS

You can add the lines you suggested, but it won't have any effect. Software needs to be programmed to read those environment variables, and I doubt that Ubuntu One reads XDG_UBUNTUONE_DIR, or that Dropbox reads XDG_DROPBOX_DIR.

You can, however, specify icons for folders using Nautilus. This used to be a built-in feature of Nautilus, but for the newer versions, you have to install an add-on. See: Is there any tweak to bring back emblems in Nautilus?