Gave up trying to get Hyper-V Server 2012 to work…

http://blogs.technet.com/b/klince/archive/2010/09/13/booting-hyper-v-r2-from-a-bootable-usb.aspx

http://www.itstuff.ca/2009/12/create-bootable-usb-drive-for-hyper-v.html

• Boot Hyper-V Server from USB flash devices
• Saves hot-swap drive bay for storage
• 16GB Flash device recommended
  • Get the fastest one you can
  • This device will be wiped and any data lost

During this procedure, carefully keep track of the disk numbers, partition numbers and drive letters. A mistake can ruin your whole disk!

1) Download and install WAIK: http://www.microsoft.com/en-us/download/details.aspx?id=5753

2) Download the Hyper-V Server .iso file

3) Mount the Hyper-V Server .iso file (G: used here for mounted .iso file)

• Free tool to mount .iso files

4) Create, mount and prepare the VHD (virtual hard disk) that will become your bootable USB flash drive. Open a command prompt as administrator:

diskpart

create vdisk file=c:\virtualharddisk.vhd maximum=6000 type=fixed
select vdisk file=c:\virtualharddisk.vhd
attach vdisk
list disk
select disk 1 (select the newly created VHD)
create partition primary
select partition 1
active
format fs=ntfs quick
assign letter=x
list volume

5) Apply the install image to the VHD. Leave the “diskpart” window open and open another command prompt as administrator.

• Change into the appropriate directory (x86 or amd64) based on the architecture of your technician workstation

cd "C:\Program Files\Windows AIK\Tools\<arch>\"
imagex.exe /apply g:\sources\install.wim /check 1 x:\

6) After that finishes, switch back to the “diskpart” command window (where diskpart is still running) to prep the USB flash drive:

list disk (to determine the disk number of the USB flash drive - '2' used here)
select disk 2
clean
create partition primary
select partition 1
active
format quick fs=ntfs
assign letter=z

7) Switch back to the “imagex” window and copy 'boot' files from the VHD to the USB target disk:

bcdboot x:\Windows /s z: /v

8) Switch back to the “diskpart” window and dismount the VHD file:

detach vdisk
exit