If I am correct, the runs off a timing relay, not a basic relay. You would either need to find a blinker relay that is NC or you would need to add a relay and modify the wiring a bit for it to work.
You would want to take the POS in from the timing relay, splice it, and connect it to the common on NC connection opposite the common. The common would then run to the blinkers. The output from the timing relay would run to the POS leg of the relay coil.
I am doing this in my head, so I may be off a bit, feel free to correct.