mkusb : mkusb is an ISO multiboot USB tool with support for Legacy/EFI x86/amd64 ( https://github.com/fkmclane/mkusb )
mkwin : mkwin is a tool for creating a bootable USB from a Windows ISO ( https://github.com/fkmclane/mkwin )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a fkmclane
For Paludis use this rsync : rsync://gentoo.zugaina.org/fkmclane-portage
If you have a problem : ycarus(-at-)zugaina.org