As you know, Fedora 19 Alpha has been released.
To install XFCE on Fedora 19, just open a terminal and type:
$ sudo yum install @xfce
To disable the always-on-top behaviour of XFCE panel do this:
$ xfconf-query -c xfce4-panel -p /panels/panel-/disable-struts -t bool -n -s true
This is it. Reboot and Enjoy.