Would you like to try Xfce 4.10pre2 ? Are you running Xubuntu 12.04 beta/pr? In case of 2 positive answers, you are only one PPA away from your goal.

- use your terminal to type:

sudo add-apt-repository ppa:mrpouit/ppa
sudo apt-get update
sudo apt-get dist-upgrade

- if you decide to remove Xfce 4.10pre2, type these:

sudo apt-get install ppa-purge
sudo ppa-purge ppa:mrpouit/ppa

(Note: Keep in mind that this is not a final/stable Xfce 4.10 release, but a preview release 2 - also, you would be testing a Preview Release in a Beta... so, if you do proceed, do so with caution! & expect some rough edges)