Urban, whilst that is a logical approach, it is not that easy, unfortunately. One of the many ‘quirks’ of the system design means that when you have bought membership, you are then tied down to that card number, address, and account. If you cancel a cycle hire account, your information is kept on the system, and you will not be able to use that any cards tied to that bank account again.
There are also issues with registering multiple accounts under the same address. So unless you have another bank card you can use, and another address, best bet is to just suck it up and pay double next year. It will still prove to be better value than using the bus, tube, or (if you are crazy enough to use it to get around Central London) car.