Macos – how can I make a USB stick bootable in EFI

https://wiki.archlinux.org/index.php/ThinkPad_Edge has the process:

1. Grab and unpack https://gna.org/projects/grub4dos/ (the wiki has an old link)
2. In the grub4dos directory, sudo ./bootlace.com /dev/sdb
3. cp grldr /media/USBSTICK
4. cp menu.lst /media/USBSTICK
5. cp /path/to/7yuj40uc.iso /media/USBSTICK

Finally you have to add the following code to the menu.lst on your pendrive to make the USB-Stick boot the PC DOS program made by lenovo:

title Thinkpad-BIOS-UPDATE
find --set-root /7yuj40uc.iso
map /7yuj40uc.iso (0xff) || map --mem /7yuj40uc.iso (0xff)
map --hook
chainloader (0xff)
boot

And that's about it.

Have you tried "Acetoneiso"?

It'll convert the DMG to an ISO for you. After that, the easiest way I know of to make a bootable USB is using DD.

dd if=/path/to/osx.iso of=/dev/sdX && sync

Note: sdX is an example, you will have to check your flash drive address (usually sdb if you have only one hard disk). Do not add a partition # after that (such as sdb1). This method is a little hard on flash drives (I have killed one or two doing this relatively frequently, but once should be fine).

If you are unfamiliar, DD is a bit by bit copy and sync just verifies that all files have been written to the usb.