I need to create a LiveUSB Linux image on a USB hard drive?

Specifically I want to create a full linux install on the USB hard drive but with the full driver detection capabilities of a LiveCD. I don’t want to emulate a livecd on the usb hard drive as that creates a ramdrive and is not persistant if I make changes to the config files, etc. without mounting another partition and storing a config file. Can this be done? I was able to install Ubuntu onto a USB hard drive (full install) but now I need to add in the driver detection capabilties and have it autoupdate the xfree86config files etc. like a LiveCD would. Does anyone know how to do this?