3.5mm Microphone and earpiece

Is it possible to use this app so that when I am in a call, I can set it to use the microphone from a headset, but play sound through the earpiece?

The built in microphone is broken, and I have a small microphone that sits in the 3.5mm jack, but android tries to send audio to the non existent speakers that would be present.
This app looks very promising, I have been able to make incoming sound go to the earpiece, but then the microphone doesn't work.

Is what I want possible to do? Is it something that could be added if it isn't already?

I've tried this.

Android won't allow splitting a device (headset) mic from it's corresponding audio output (headset speaker).  I can only do this with Bluetooth mono device while NOT in a phone call to use it for voice recognition.