Frankly, I can't answer that question. First, not all computers, even newer ones, can boot on a Flash Drive or any other USB device. If it isn't in BIOS, it can't boot there. So, that is a limiting factor in any case.

However, a rather interesting development. Google for puppy linux, a small distro that seems to be capable of doing almost anything (?)

On the URL (www.goosee...) somewhere is a How-To that claims to make it possible to boot on any USB including flash drives. There is a boot floppy iso available via ibiblio which loads USB drivers during floppy boot, and then system.com (?) or whatever you call it looks at all available drives, including flash USB. This apparently includes those USB devices that are on computers which will not boot on USB, but will vary depending upon whether USB drivers work on your machine.

I have not tried it, but they seem confident. I must wonder if it is possible to change the system file to look for other distros. Good project for someone who has more internet access than I do.