A resistor would only limit current not voltage. Think of it this way if you have a hose and it has a restrictor placed in line with it very little water will come out the end limiting flow (amps), but if you plug the end the pressure (voltage) will rise to the same as before the restriction. So when the current draw is near 0 the voltage will rise to a dangerous level and take out the RX and servo.
Brian this would be easy to add to the existing BEC on the board. Good idea using the fuse, I figured that the trace would be good enough.
Jeff