Well, I would measure the resistance of a normal bulb. Then get a resistor of the correct value, cut the wire that feeds the light cluster for the indicator power and then solder the resistor inline with the wire. This would have to be done on both rear indicators.
I bought a set of the nismo led tailights and have been getting the same problem. It happens on an off, on the left side only. The front left indicator flashes quickly and when brakes is applied, the rear tail lights blink.