Boot from a USB stick if BIOS doesn't support USB boot!

Not normally possible!

However, this question intrigued me and I've done a bit of research as I have not looked at the subject in a while.

Turns out there appears to be a German programmer who has built a piece of software that boots from a floppy or cd and allows one then to boot from a usb stick.

There is an excellent walk through published on howtogeek.com here.

http://www.howtogeek.com/howto/16822/boot-from-a-usb-drive-even-if-your-bios-wont-let-you/

The article has links to the necessary page for downloads.

Not tried it myself but hope it it is appropriate for your needs.