Your traditional method of putting each heater line through one resistor to drop excess voltage is the best way to go. That method actually reduces the current load on the transformer while it reduces the voltage reaching the tube heaters.
The other proposed method of reducing the virtual center tap resistance to load the transformer winding and thus reduce voltage is very bad practice for several reasons.
1) Increases stress on the transformer
2) Increases heat dissipated inside the chassis
3) Requires higher wattage / more expensive resistors
4) Just plain inefficient. It is analogous to reducing the speed of your car by riding the brake rather than letting up on the accelerator.