You should be able to just "clone" the sim and it should work. Unless they lock the sim/your account to a particular handset, but even in that case, you can probably have them just add the serial ID for the 2nd phone to your account.
As far as I am aware, they don't care how many phones you have with the same number, they all pull from the same account.
I know it works the other way around when you "splice" two sims into one phone and you can have two numbers, or even two providers, for one phone.