Is this your first extension or are you switching from banked funds method to monthly funds method? In short you can't use the monthly method for your first extension.
Are you applying in the same country as that employment contract document comes from? If so I'm sure they would recognize a standard contract. What language is it in?
There are no requirements from other immigration or banking to have a year lease, immigration might want to see it, the bank may require that for you to open up an account but what you do after that day totally up to you