In theory it's doable if your BIOS supports booting from the USB drive. However mine does and although I've never tried this specific method every other one I've tried just doesn't work and I know a few others who have the same problem.. whereas for others the USB boot option does work.

There's really no harm in trying though since if it doesn't it hasn't cost you any money and the drive can be easily reformatted and reused.

Worth noting is that the Hiren's CD they refer to no longer contains illegal software as of over a year ago so that option is still available to try legally if you use the most recent version(s).