How to use OK google in my car? (Screen off AND unpugged)

[CreepyD]

I was looking forward to 5.0 on my LG G3 as I heard it would allow you to use Ok Google with the screen off.
Finally I will be able to tell my phone to navigate somewhere or change the music that's playing without taking my phone out of my pocket.

I already have it automatically connect to my car's bluetooth and can make phone calls through the built in mic, and play music through the sound system.
It works fantastically, except I can't tell the phone to navigate or do other things I 'should' be able to do really by using Ok Google.

Turns out the phone still has to be plugged in to use Ok Google with the screen off, and even then it doesn't seem to listen through the car's bluetooth connected mic, despite me turning on the setting in Google to use a Bluetooth connected mic - I have to hold it right up by the wheel (Tested while not driving! )

I tried OpenMic+ but it really didn't work well at all.

So is there any way around this at all other than wasting time plugging it in every journey?

I'm not rooted either (can't - It's a work phone).

Thanks very much for any replies