Controlling S2's microphone volume on headphones

[davidair]

I can use my S2?s 3.5 jack to output audio to the car speakers via the cassette adapter ? works fantastically well. However, there is an annoyance when using this setup for taking calls: when the phone is on Speaker, the audio does not stream via the headphone jack, the microphone volume is high. When the phone is off speaker, the call streams through the car?s speakers (awesome!) but the microphone?s volume is much lower.

Is there a way of making the microphone volume higher when the 3.5 jack is connected? This setup is a much cheaper alternative to the Bluetooth car kit!