Hey that's a great idea, OldFred, a Grub over BCD boot disk!
GRUB 2 supports the NT file system, so that would be entirely feasible. I have even installed GRUB inside Windows in the past. There are only two commands needed to turn it into a standalone GRUB/BCD boot disk. A boot disk like that could be made from the Ubuntu LiveCD before a person begins installing Ubuntu.
Lets see now, in my Ubuntu installation the Windows 7 boot loader partition in the USB shows up automatically mounted as /media/System Reserved.
This can either be verified by the ls /media command, or by navigating to the /media folder with the file manager and taking a look.
Linux doesn't like white spaces, so I need to use GParted to change the label in that file system and replace the white space with an underscore or a hyphen. (requires nyfsprogs to be installed first).
Now it's showing up as as /media/System_Reserved.
Using the blkid command to check, the partition number is /dev/sdc2, so the MBR to install GRUB to will be /dev/sdc. I can use that in the following command to create GRUB/BCD boot disk,
NOTE: To anyone wanting to try this, It is very important to check and make sure you will be installing GRUB to the correct MBR, (shown here as /dev/sdc for me in this computer), this varies between different computers and a mistake here could be disasterous for some people. You need to use the blkid command first to check.
sudo grub-install --root-directory=/media/System_Reserved /dev/sdc
Now all I need to do is copy my current grub.cfg to the new boot disk,
I just tested the new boot disk and it appears to be working on the first test boot-up and has booted Windows 7 okay. I will likely get to test it a few more times as the next items on my agenda are to be risky for Windows 7. In fact I have already trashed the Windows 7 boot, I deleted my hard disk Windows 7 bootloader partition and 'm going to try that Booting Windows Vista/7 From a Logical Partition tutorial again.
sudo cp /boot/grub/grub.cfg /media/System_Reserved/boot/grub/grub.cfg