Cutting the PVC pipe and then re-assembling with a proper PVC coupling is one option. It might also be feasible to cut one of the copper lines and remove the pipe from the heater so that the blower can move sideways enough to get at the anode rod.
Standard plumbing rubber banded couplings are not approved for that use. The flue gas can damage some materials. An HVAC supply might have something that is, but I not aware of one.