Your spacer is (or at least should be) matched to either the hub bore on the wheel or the car.
Assuming it is, a hubcentric ring will work just fine since it'll sit flush with the inside/outside of the spacer depending on if it is matched to the car or the wheel.
http://www.ecstuning.com/Volkswagen-Jetta_V--2.0T/Wheels/Hub_Centric_Rings/ES2200633/
