Comment by SysArchitect

This still has the issue of not being able to use your car controls to control the music, but:

https://www.amazon.com/Antec-Portable-Bluetooth-Receiver-Hea...

Pair this with your phone, and plug it into power. When your car turns on, it powers on, pairs with your phone, and spits audio out over 3.5mm to the car stereo.

Comes with a 3.5mm male -> 3.5mm male plug for this purpose.