Using multiple USB drives would be the most straight-forward way to do this yes, but what I 'think' you might be able to do is make a bootable USB stick using something like Caldera DrDos and then boot to a command prompt and execute the setup for the Windows variety of your choice ...or what is more likely to work would be to complie a bootable USB stick with the Windows Preinstallation Environment and do it via that.
I don't know if this will work or not, I'm just spitballing really, but it might.