Actually, there is a convenient way which I used today. I had to format and reinstall windows too. But MnB was on other partition. I knew that registry would be wiped out, and most programs on other partitions would not be detected as 'installed'.
What I did was: I opened registry, found MnB keys (MnB directory plus another one that has key validation), then I exported each to a file which I put on the other partition.
After windows reinstall, I simply double-clicked these two files and that was it. MnB works normally without having to install it again.
Now, the problem is, if you didn't do this before formatting HDD, not much you can do I'm afraid.