This isn't exactly the answer you were looking for, but it's what I'd recommend. Unless there is a pressing reason to dual boot a single drive, and presuming we're talking a desktop model rather than a laptop, consider getting another HDD, removing your Windows 7 drive, and doing a straight clean install of F12 on the new drive.
Then your Windows drive can be put back in, none the wiser to the adventure, and your F12 grub can be set up to boot into Windows if needed.
Pros: No accidental harm can come to existing data.
No re-install of Windows needed if something does go wrong.
More storage space (by default)
A clean F12 install will take less time.
Cons: A little hardware time and experience is needed.
Another drive will cost money.
You'll need to hand edit your F12 Grub for "dual boot" capability.