How to stream music from one phone to another?

Myself and guy at work both have Samsung Galaxy S3's.

We both have radios with audio-in.

We want one person (me) to play mp3s, and for it to stream over to other guy's phone, so we can both be listening to the same stuff in stereo (his workstation is about 30ft from mine). LOUD shop (factory) so I can't just turn the volume up and blast it over to him.

Is there a way for my phone to stream all it's audio over to his?

With the deck/head-unit in my truck, I just pair my phone with it, and my truck plays all the audio from my phone through it's sound system. Doesn't work when we pair our phones via bluetooth.

Ideas??

 

Ooh, and that Bluetooth Music Player app doesn't work...

Still looking for ideas.

You'd think with all the 'sharing' convenience that Android and especially Samsung are always promoting, that this would be possible.