change windows partition device number as reported by cygwin stat

I have two partitions with the same device number:

$ stat -c "%D" /cygdrive/c
ec86b9d9
$ stat -c "%D" /cygdrive/g
ec86b9d9

I believe this is because G: was restored from an image of C:. C:cygwin64 is mounted on /. When I try to run diff -r / /cygdrive/g/cygwin64 then it skips over directories with the same device + inode number. This is not a bug in diff, per this bug report:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=33467

So how can I change the device number for the G: partition? I tried using gdisk 1.0.4 but no luck; the unique disk and unique partition GUID’s were already different in each case.

I’m using Windows 7 Bootcamp and the partitions have the same device number as each other in OS X 10.6.8 as well, although they are different from the Cygwin device number.