Afaik, its not possible
For the simple reason that, BURNING really means 'burning/"writing on" the Disk', this is NOT possible for a flash drive jus bcoz there is NO burner available,
however, u can carry the ISO image file with u along with a virtual drive s/ware like Nero image drive (comes with NERO), Daemon tools, alcohol etc..etc... and then use it on a system u intend to, but then also, its no USE (if the system doesn't allow booting from a UBA and tat too from an IMAGE ISO file..)
Best way, burn it (literally, the recorder writes data onto the disk by creating pitts (only) and crests )..
Cheers n e-peace....