Boot via USB Flash Drive

I've been seeing instructions for placing OS installation media on USB flash drives for ease of use, but utilization of one of those might require booting from the USB flash drive.

On page 9 of "Parallels Desktop Adanced VM Configuration", it says, "The BootingOrder node has child elements called BootDevice, each of which defines an individual boot device." A list of those devices is shown on page 10 of that document, and one of those devices is "PDE_USB_DEVICE"; however, it also says, "(this is the complete list, not all items are applicable here)". So, not all the devices are bootable, and of course one would not expect to boot from sound, printer, etc, non-disk devices. However, it's not clear to me whether "PDE_USB_DEVICE" can be used as a bootable device. Does anyone know whether it can, or not? Is it possible to boot from a USB flash drive in Parallels 8?

Thanks,
Bev in TX