Ubuntu

There's not a magic "make-flash-drive-act-like-bootable-CDROM" program; even if you fooled the BIOS somehow, everything'd break down the instant things started loading device drivers. It's possible to mount the ISO as a loop device though, but then the programs on disk would start pining for a CDROM drive of some sort. Unless you specifically told them somehow that they were to use this disk image instead, and the programs on the ISO had the ability to use such options. So making a USB-based installer is pretty much tantamount to either 1) installing it on the USB drive, or 2) extracting the contents of the ISO onto it and modifying them by hand, or 3) Dumping the images on it, installing a bootloader and the correct kernel+modules+initrd, and using special distro-specific boot options to allow it to use a given ISO image instead of a cdrom.

So all of these are distro-specific, and all of these are going to be pretty difficult when he can't get the information out of the the ISO. There's not a generic solution.

Yes, you need bios to boot a USB pen drive, or you have to boot a "pen drive boot program" from a supported boot device.

Hiren's BootCD From USB Flash Drive (Pen Drive) - www.hiren.info
Use a Boot CD to Boot from USB | USB Pen Drive Linux

I recall some LINUX demos used to boot from Windows, taking over the machine already running, replacing the O/S on the fly! It beats putting in a paper tape loader one bit at a time.