IOS: Audio IN via connector, audio output through built-in speaker

Question

My project uses a magnetic card reader that connects to the background connector (i.e. uses only a microphone)

Can I get my project to output sound through the built-in speaker while listening to input from the device?

Studies show that this is not possible:

IPhone audio playback: power through the internal speaker?

Force iPhone to output through speaker while recording from headphone microphone

Audio Session Services: kAudioSessionProperty_OverrideAudioRoute with various input and output routes

The only way I see it is to actually change the audio session every time I want to emit sound.

Is this really the only option? And is it practical to do this? How long does it take for an audio session to reconfigure itself?