Cloning your wallet to do anything besides backing it up is a bad idea.
It might work perfectly for a while... but you are very likely to get weird behavior from bitcoin sooner or later, because doing that is not tested or supported.
Where 'weird behavior' is one clone of the wallet shows one balance, the other clone shows another, and you might end up with bitcoins that you can spend from one wallet but not the other (or, worst case, end up with bitcoins that neither wallet is able to spend).
If you REALLY REALLY REALLY want to do this... then get the latest code from git, pull sipa's 'Spent per txout' patch, and then spend a bunch of time testing to find out what happens when your cloned wallets eventually start using different keys from the keypool.