Post date: Jan 21, 2016 6:15:52 AM
I spent the better of my last two days trying to image a new PC with three operating systems -- two Windows, one Linux -- and have the Windows ones accessible from the GRUB menu directly, without having to deal with the chainloaded Windows Boot Manager.
Unfortunately, online research wasn't fruitful, but helped me piece together the requirements for this installation to be successful; and since it was, I found it worthwhile to share it online for whoever else is looking for it.
Make the two Windows installations agnostic of each other's existence.
Install mama Linux and have GRUB do the rest.
In my case I had to install Windows 7, Windows 2012R2 and Ubuntu 14.04. The following might or might not work with different versions; referring to Windows boot schemes... Linux is usually nice to our PCs.
Install Windows 2012R2 and use only portion of the drive, not the whole thing.
Boot from a Live Ubuntu USB or other Live USB/CD that contains GParted application. Remove the BOOT flag from the boot partition of Windows (Right-click -> Edit Flags on the FAT32 ~100MB partition called System).
Create another ~100MB partition from the unused disk space and format it as FAT32. This will be used for the MBR of the second Windows.
Create an NTFS partition where the second Windows OS will be installed on. Again, use only part of the remaining space.
Install Windows 7 on the newly created NTFS partition. By turning of the BOOT flag on Step 2, the second Windows installation is not aware of the first one, and therefore will use the newly created (Step 3) space to place its MBR on.
Use the Live Ubuntu USB and GParted to turn the BOOT flag back ON. At this point, you should have two Windows installations, each with the own boot partition. Since the two installations are not aware of each other, the system will only boot to one of the two (not sure how this is determined, but it can be changed in BIOS if needed).
Lastly, install Ubuntu, which will scan the entire drive for Windows juice and detect "multiple OS installed" and present an option to install along them, without losing files etc.
After installation finishes, GRUB should detect Ubuntu (ba dum tss!) and two instances of Windows Boot Manager, each on a different partition. Use grub-customizer to edit their names to their respective OS names.
There is no Step 9. It just makes it feel like there's three 3-step parts to this. Fooled ya!