How does iPhone detect when dock connector is connected to an audio input?
Potentially it may work and should be safe, although resistors of lower value than headphone impedance (32 ohms) could theoretically be damaging. I would try 100 ohms and 50 ohms first. Standard 1/4 watt resistors will do. Note there will be a loss in signal amplitude through the resistor. Make sure you avoid the possibility of shorting out the wires by careful construction.