It's doable, and it's already done...
All it matters is you take the other nand, decrypt it with that console's special keys, and re-encrypt it with your console's keys...
Don't ask me, I don't know the actual details...
ps: oops sorry, this guy possibly used two distinct backups of his one system... one on 3.1 and one on 3.2... though still I think it's doable...