This is my EFI boot configuration using Grub 2.00 for booting Ubuntu, Windows 8.1 and Mac OS X.

This configuration lets me boot Windows and Ubuntu from external USB3 drive from Mac boot menu.

NOTE: Windows has to be installed via Parallels since only Enterprise version allows direct installation on selected USB drives.

Installing via Parallels workarounds that. Booting Windows can be done from any drive however.

Configuration uses Mac Grub 2.00 theme made by myself, that works best on FullHD or Retina displays.

Just checkout this repository into some HFS+ or FAT32 partition on GPT partitioned drive into /efi/ root directory, i.e.:

cd /Volumes/Boot
git clone https://github.com/nanoant/efi.git

Use Parallels with "EFI Boot" option enabled or reboot your Mac keeping Option pressed.

Adjust boot/grub.cfg to match your settings.

1. Setting boot icon is as simple as putting .VolumeIcon.icns file onto partition containing /efi/ folder.

2. Setting boot label can be done with

   bless --folder /Volumes/Boot --label NameOfOS
   

bless --folder /Volumes/Boot --nextonly

1. Create ~100 MB FAT32 boot partition, set its GUID to efi

2. Copy whole /efi/ folder from Windows USB flash drive installation made by Bootcamp to that partition.

3. Boot into USB flash drive installer and press Shift+F10 for command prompt.

4. Mount your EFI boot partition with diskpart

   DISKPART> list vol
   DISKPART> sel vol EFI_INDEX
   DISKPART> assign letter=b
   

5. Regenerate BCD store with:

   cd /d b:\EFI\Microsoft\Boot\
   bcdboot c:\Windows /l en-gb /s b: /f ALL
   

Now you should be able to boot directly to Windows from Mac EFI menu.

This software is provided under MIT license:

Copyright (c) 2012 Adam Strzelecki

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.