While Googling for the same desire (instead, I have Linux/Win as dual boot available hosts) considering to abuse Yumi for it.
I found Easy2Boot, which looks promising.
Here's a forum topic about the Easy2Boot tool including YouTube video:
- http://www.msfn.org/board/topic/162640-install-all-windows-install-isos-from-1-multiboot-usb-drive/
- https://www.youtube.com/watch?v=MBKh_jDyTmQ
- https://www.youtube.com/watch?v=YyQ7xSvVMHE
I'm about to try it out.
You could use the opensouce Virtualbox to get Windows running inside OS X